* When new uid is seen in join attempt we can down existing
member and thereby new restarted node will be able to join
in later retried join attempt without relying on auto-down.
* 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
