Beta2 release of UberFx

* [Breaking] Remove `ulog.Logger` interface and expose `*zap.Logger` directly.
* [Breaking] Upgrade `zap` to `v1.0.0-rc.3` (now go.uber.org/zap, was
    github.com/uber-go/zap)
* Remove now-unused `config.IsDevelopmentEnv()` helper to encourage better
  testing practices. Not a breaking change as nobody is using this func
  themselves according to our code search tool.
* Log `traceID` and `spanID` in hex format to match Jaeger UI. Upgrade Jaeger to
  min version 2.1.0
  and use jaeger's adapters for jaeger and tally initialization.
* Tally now supports reporting histogram samples for a bucket. Upgrade Tally to 2.1.0
* [Breaking] Rename `modules/rpc` to `modules/yarpc`
* [Breaking] Make new module naming consistent `yarpc.ThriftModule` to
  `yarpc.New`, `task.NewModule`
  to `task.New`
* [Breaking] Rename `yarpc.CreateThriftServiceFunc` to `yarpc.ServiceCreateFunc`
  as it is not thrift-specific.
* Report version metrics for company-wide version usage information.
* DIG constructors now support returning a tuple with the second argument being
  an error.

Initial beta release of UberFx