Updated dependencies.

Removed rendering of `CDATA` tags, it now just removes them.

Merge branch 'master' of github.com:hexydec/cssdoc

Added `@layer` directive to list of nested directives.

Updated `directive::parse()` to set a new `empty` property, for detecting when a directive has curly brackets, but no content, enabling directives with just properties not to be deleted.
Added tests.
Updated dependencies.

Split config into its own file and extended `cssdoc`.

Updated type hints to correct types where `#[\ReturnTypeWillChange]` …

…as the software now only supports PHP 8.0+.

Added type hints where `mixed` is required.
Added union type hints on arguments and return types where missing.
Commented out new code that is not working yet.

Fixed issue where key() must return mixed in PHP8.1. It is now marked…

… as #ReturnTypeWillChange.

Fixed status badge in readme.md.

Removed the type hint `mixed` as it is not compatible with PHP 7.4.

Added #[\ReturnTypeWillChange] to methods that return mixed for PHP 8.1 compatibility.
Fixed some docblock issues.
Updated usage of `str...` functions to be `mb_str...`.
Fixed issue in `value::minify()` where if the `decimalplaces` setting was false it would be treated as `0`.
Added tests.

Updated dependencies.