* deprecates awaitTermination, shutdown and isTerminated
* introduces a terminate-method that returns a Future[Unit]
* introduces a whenTerminated-method that returns a Future[Unit]
* simplifies the implementation by removing blocking constructs
* adds tests for terminate() and whenTerminated
* because it is not referentially transparent; normally we reserved parens for
side-effecting code but given how people thoughtlessly close over it we revised
that that decision for sender
* caller can still omit parens
* Replace (deprecate) akka.cluster.auto-down config setting with
akka.cluster.auto-down-unreachable-after
* AutoDown actor that keeps track of unreachable members
and performs down from the leader node when they have been
unreachable for the specified duration
* Migration guide
* Deprecate all actorFor methods
* resolveActorRef in provider
* Identify auto receive message
* Support ActorPath in actorSelection
* Support remote actor selections
* Additional tests of actor selection
* Update tests (keep most actorFor tests)
* Update samples to use actorSelection
* Updates to documentation
* Migration guide, including motivation
