Update to 0.4

CHANGELOG:
0.4
  Added instance Contravariant Proxy

0.3
  Added Backwards and Reverse instances for transformers 0.3
  Added instance (Functor f, Contravariant g) => Contravariant (Compose f g).
  (This is non-canonical, but is necessary to support other packages.)
  Added Functor instances to ComposeFC and ComposeCF for use when modeling phantom type parameters caused mixing Functor + Contravariant.

0.2
  added missing category instance. breaks API though, so required major version bump