eff 4.0.0

New interpreters!

This version provides a generic interpreter "loop" to interpret Eff values. You just need to provide an Interpreter
trait with appropriate definitions for:

• interpreting pure values
• interpreting an effect of type M[X]
• interpreting a list of effects T[M[X]](the "applicative" case) where T has a Traverse instance
• interpreting a "last" effect, in case of having side-effects to finalize resources (see SafeEffect.thenFinally)

This new org.atnos.eff.interpret.interpret method is stack-safe provided that you never call continuations directly
but always with Eff.impure(x, continuation) (see the various effects interpreters for examples).

There are also simpler traits like Recurser or Translate, please read the scaladoc for the Interpret trait.

Changes

There are only low-level API changes

• many of the Interpret trait method have changed (interpret, intercept,...) or been removed. Please use
  the gitter channel if you have any questions

• the "continuation" type inside an Eff value has been renamed Continuation to help newcomers understand the library better

Improvements

• Eff.tailRecM is now stack-safe
• the catbird and twitter-util dependencies have been updated (thanks to Chris Vale)
• EitherEffect.attemptEither will attempt an Either effect and return E Either A
• EitherEffect.runEitherCatchLeft will run an Either effect and handle the resulting E Either A value in case of a
  failure