* Receive class that wraps PartialFunction, to avoid
scary scala types
* move AbstractActorContext to AbstractActor.ActorContext
* converting docs, many, many UntypedActor
* removing UntypedActor docs
* add unit test for ReceiveBuilder
* MiMa filters
* consistent use of getContext(), self(), sender()
* rename cross references
* migration guide
* skip samples for now
* improve match type safetyi, add matchUnchecked
* the `? extends P` caused code like this to compile:
`match(String.class, (Integer i) -> {})`
* added matchUnchecked, since it can still be useful (um, convenient)
to be able to do:
`matchUnchecked(List.class, (List<String> list) -> {})`
* eleminate some scala.Option
* preRestart
* findChild
* ActorIdentity.getActorRef
