Provisional release notes below. We might want to expand on the explanation of some of the breaking changes and enhancements, so any suggestions welcome. I'm going to be out until later tonight and will make the release when I get back, unless anyone else wants to jump in before then.

Breaking changes

• Added applicative-do notation; ado is now a keyword. An full explanation of the behaviour and usage of ado is available in a comment on the issue. (Add applicative do notation #2889, @rightfold)
• Removed wrapper scripts for the old binary names (psc, psci, etc.) (Deprecate & remove old wrapper scripts #2993, @hdgarrood)
• Removed compiler support for deriving purescript-generics. purescript-generics-rep is still supported. (Remove old generics and generics-rep record support #3007, @paf31)
• Instances with just one method now require the method to be indented (bug fix, but potentially breaking) (Instances with just one method do not require that the method be indented #2947, @quesebifurcan)
• Overlapping instances are now an error rather than a warning, but can be resolved with the new instance chain groups feature (Instance chains #2315, @LiamGoodacre)
• Reworked the CoreFn json representation (Corefn Json representation #3049, @coot)
• It is no longer possible to export a type class that has superclasses that are not also exported (bug fix, but potentially breaking) (Disallow hiding superclasses of exported classes #3132, @parsonsmatt)
• Eq and Ord deriving will now rely on Eq1 and Ord1 constraints as necessary where sometimes previously Eq (f _) would be required. Eq1 and Ord1 instances can also be derived. (Eq1 / Ord1 deriving again #3207, @garyb)
• Some Prim type classes have been renamed/moved, so will require explicit importing (Rename prim classes #3176, @parsonsmatt):
  • RowCons is now Prim.Row.Cons
  • Union is now Prim.Row.Union
  • Fail is now Prim.TypeError.Fail
  • Warn is now Prim.TypeError.Warn
• Users can no longer specify modules under the Prim namespace (Disallow Prim modules #3291, @parsonsmatt)
• TypeConcat and TypeString have been replaced because they were in kind Symbol but weren't literals. The Prim.TypeErrer.Doc kind and related constructors (Text, Quote, Beside, Above) have been added in their place. The Fail and Warn type classes now accept a Doc instead of a Symbol.
  (Fail, TypeConcat, & TypeString shouldn't end in kind Symbol #3134, @LiamGoodacre)
• In simple cases instance overlaps are now checked at declaration time rather than being deferred until an attempt is made to use them. (Check that instance declarations don't overlap #3129, @LiamGoodacre)
• Chaining non-associative or mixed associativity operators of the same precedence is no longer allowed (Add real error messages for associativity errors #3315, @garyb)
• The --dump-corefn and --source-maps arguments to purs compile have been removed. There is now a --codegen argument that allows the specific codegen targets to be specified - for example, --codegen corefn will not produce JS files, --codgen js,corefn will produce both. If the sourcemaps target is used js will be implied, so there's no difference between --codegen js,sourcemaps and --codegen sourcemaps). If no targets are specified the default is js. (Add flag to disable Javascript backend #3196, @garyb, @gabejohnson)
• Exported types that use foreign kinds now require the foreign kinds to be exported too (bug fix, but potentially breaking) (Check foreign kinds are exported when used in exported type #3331, @garyb)

Enhancements

• Added Cons compiler-solved type class for Symbol (Solve ConsSymbol #3054, @kcsongor)
• The Append compiler-solved type class for Symbol can now be run in reverse (Run AppendSymbol in reverse #3025, @paf31)
• purs ide treats hiding imports the same as open imports when sorting ([purs ide] Groups hiding imports with implicit ones #3069, @kritzcreek)
• Added inlining for fully saturated usages of runEffFn/mkEffFn (Add inlining for runEffFnN/mkEffFnN #3026, @nwolverson)
• Improved explanation of UnusableDeclaration error (Expand error message for UnusableDeclaration #3088, Tidy up "undetermined class argument" warning #3304, @i-am-tom)
• Improved rendering of comments in generated JavaScript by removing additional newlines (Empty lines between comment lines  #3096, @brandonhamilton)
• Instance chain support. (Instance chains #2315, @LiamGoodacre)

  We can now express an explicit ordering on instances that would previously have been overlapping.
  For example we could now write an IsEqual type class to compute if two types are equal or apart:

  class IsEqual (l :: Type) (r :: Type) (o :: Boolean) | l r -> o
  instance isEqualRefl :: IsEqual x x True
  else instance isEqualContra :: IsEqual l r False
  

  Note the else keyword that links the two instances together.
  The isEqualContra will only be up for selection once the compiler knows it couldn't possible select isEqualRefl - i.e that l and r are definitely not equal.

• Improved orphan instance error to include locations where the instance would be valid (Add valid location list to orphan instance error #3106, @i-am-tom)
• Added an explicit error for better explanation of duplicate type class or instance declarations (Misleading error with name conflicting instances #3093, @LiamGoodacre)
• purs ide now provide documentation comments ([psc-ide] Collect docstrings for identifiers #2349, @nwolverson)
• Clarified meaning of duplicate labels in a Record row (Add docs for duplicate labels in record types #3143, @paf31)
• Explicit import suggestions consistently use (..) for constructors now (Make explicit import suggestions more consistent #3142, @nwolverson)
• Improved tab completion in purs repl (REPL doesn't auto-complete re-exported symbols #3227, @rndnoise)
• Large compiler perfomance improvement in some cases by skipping source spans in Eq, Ord for binders (Skip SourceSpan in Binder Eq, Ord for faster exhaustivity check #3265, @bitemyapp)
• Added support for error/warning messages to carry multiple source spans (Allow errors to carry multiple positions #3255, @garyb)
• Improved tab completion in purs repl when parens and brackets are involved (Complete after parens and brackets in REPL #3236, @rndnoise)
• Improved completion in purs repl after :kind and :type (Complete any number of words after :kind and :type in REPL #3237, @rndnoise)
• Added the "magic do" optimisation for the new simplified Effect type (Control.Monad.Eff is still supported) (Implements magic-do for Control.Monad.Effect #3289, @kritzcreek, Update Effect inlining #3301, @garyb)
• Improvide build startup times when resuming a build with incremental results (Smarter make #3270, @kritzcreek)
• Added compiler-solved Prim.Row.Nub type class (Add compiler derived Prim.Row.Nub class #3293, @natefaubion)
• Improved docs for Prim.Row.Cons and Prim.Row.Union (updated docs for RowCons and RowUnuon #3292, @Vladciobanu)
• Functor can now be derived when quantifiers are used in constructors (Functor deriving should support quantified arguments of a constructor #3232, @i-am-tom)
• purs repl will now complete types after :: (Complete type identifiers following '::' in REPL #3239, @rndnoise)
• Added compiler-solved Prim.Row.Lacks type class (Add Prim.Row.Lacks constraint #3305, @natefaubion)
• Added current output path to missing output error message from purs ide (Add missing output directory to error #3311, @rgrinberg)
• Improved parser error messages for .purs-repl (Trailing blank line in .purs-repl fails, with a confusing error message #3248, @rndnoise)
• require in generated JavaScript now includes full index.js file paths (Change the require path in the JS output of psc #2621, @chexxor)
• Added more compiler-solved type classes and supporting types and kinds to Prim:
  • Prim.Ordering module with kind Ordering, type LT, type EQ, type GT
  • Prim.RowList module with class RowToList, kind RowList, type Nil, type Cons
  • Prim.Symbol module with class Compare, class Append, class Cons
    (Move solved type classes into Prim modules & bump test deps #3312, @LiamGoodacre, @kritzcreek)
• Generated code for closed records now explicitly reconstructs the record rather than looping (Efficient object updates for closed records #1493, @fehrenbach, blog post with more details)

Bug fixes

• Fixed a bug with names cause by Prim always being imported unqualified (Type shadowing error #2197, @LightAndLight)
• Fixed overlapping instances error message to reflect its new status as an error (Update Overlapping instances error message. #3084, @drets)
• Added source position to TypeClassDeclaration errors (Add position to type class declaration error #3109, @b123400)
• Fixed entailment issues with skolems and matches in the typechecker (Fix entailment issues with skolems and matches #3121, @LiamGoodacre)
• Fixed multiple parentheses around a type causing a crash (Double parens in type causes crash on master #3085, @MonoidMusician)
• Fixed purs ide inserting conflicting imports for types ([purs ide] Ide inserts conflicting imports for types #3131, @nwolverson)
• Fixed constraints being inferred differently for lambda expressions compared with equational declarations (Position of inferred constraint differs when using a lambda vs equation-style def #3125, @LiamGoodacre)
• Updated glob handling to prevent excessive memory usage (purs bundle uses too much memory #3055, @hdgarrood)
• Added position information to warnings in type declarations (Add position information to type warning #3174, @b123400)
• Fixed documentation generated for Pursuit rendering functional dependency variables as identifier links (Functional dependencies incorrectly render as links #3180, @houli)
• Naming a function argument __unused no longer breaks codegen (naming an fn parameter __unused breaks codegen #3187, @matthewleon)
• Added position information to ShadowedName warning (Add source spans to name constructors and fix ShadowedName warning #3213, @garyb)
• Added position information to UnusedTypeVar warning (Fix UnusedTypeVar missing position info #3214, @garyb)
• Added position information to MissingClassMember, ExtraneousClassMember, ExpectedWildcard errors (Fix various typeclass-related error spans #3216, @garyb)
• Added position information to ExportConflict errors (Fix ExportConflict error missing spans #3217, @garyb)
• Fixed ctags and etags generation when explicit exports are involved (ctags and etags generation foiled by explicit exports #3204, @matthewleon)
• Added position information to ScopeShadowing warning (Fix source span for a case of ScopeShadowing warning #3219, @garyb)
• Added position information for various FFI related errors and warnings (Error positions for FFI related errors #3276, @garyb)
• Added all available positions to CycleInModule and DuplicateModule errors (Take advantage of multi-span errors #3273, @garyb)
• Added position information for IntOutOfRange errors (Add source spans for literals #3277, @garyb, @kritzcreek)
• Warnings are now raised when a module re-exports a qualified module with implicit import (Improve "openness" check for re-exports #2726, @garyb)
• purs repl now shows results for :browse Prim (:browse Prim does not work #2672, @rndnoise)
• Added position information to ErrorParsingFFIModule (Add some source span to ErrorParsingFFIModule #3307, @nwolverson)
• Added position information for ScopeConflict cause by exports (Add positions for ScopeConflict caused by exports #3318, @garyb)
• Added position information to errors that occur in binding groups and data binding groups (Location missing from KindsDoNotUnify for recursive function #3275, @garyb)
• Fixed a scoping issue when resolving operators (Can't use an operator shadowed by a variable of the same name as the aliasee #2803, @kritzcreek, @LightAndLight)
• Type synonyms are now desugared earlier when newtype deriving (Type synonym is partially applied when derive newtype instance #3325, @LiamGoodacre)
• Fixed subgoals of compiler-solved type classes being ignored (Subgoals of compiler solved type classes get ignored #3333, @LiamGoodacre)
• Added position information to type operator associativity errors (Ensure associativity error in type operators doesn't crash #3337, @garyb)

Other

• Updated installation information to include details about prebuild binaries (Added pre-built installers to INSTALL.md #3167, @MiracleBlue)
• Test suite now prints output when failing cases are encountered (Print error message on failed examples #3181, @parsonsmatt)
• Updated test suite to use tasty (Switch test suite to use tasty #2848, @kritzcreek)
• Improved performance of repl test suite (Make REPL completion tests faster #3234, @rndnoise)
• Refactored let pattern desugaring to be less brittle (Make Let-Pattern desugaring less brittle #3268, @kritzcreek)
• Added makefile with common tasks for contributors (Makefiles make things easier for new and regular contributors alike #3266, @bitemyapp)
• Added ghcid and testing commands to makefile (Add a Makefile with ghcid and testing commands #3290, @parsonsmatt)
• Removed old unused MultipleFFIModules error (Remove MultipleFFIModules error code #3308, @nwolverson)
• mod and div for Int are no longer inlined as their definition has changed in a way that makes their implementation more complicated - Change mod for Int purescript-prelude#161 (Remove inlining for mod for Int #3309, @garyb)
• The test suite now checks warnings and errors have position information (Check warnings/errors for positions #3211, @garyb)
• The AST was updated to be able to differentiate between let and where clauses (Track where clause metadata #3317, @joneshf)
• Support for an optimization pass on CoreFn was added (add a CoreFn optimization pass #3319, @matthewleon)