* 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
* Re enabling Java tests in akka-docs (they were not run before)
* Fixed bug #19764
* #19735 Rewrote every sample using the deprecated PushPullStage and friends
using GraphStage
* Pruned old unused graph images
* Added missing graffle file for new graph images
* Added LogEvent subclasses with new field for transporting the MDC custom values.
* Slf4jLogger now takes MDC values from new LogEvent field, puts all in MDC before appending the log, and removes all after.
* New trait DiagnosticLoggingAdapter was introduced, which extends LoggingAdapter and adds MDC support with methods to get, set and clear MDC values.
* New factory method added to Logging for getting loggers with MDC support.
* BusLogging was changed to create new LogEvents including the MDC values.
* Actors can mixin with DiagnosticActorLogging which defines a diagnostic logger "log", has a hook to override for defining MDC values per message, and overrides aroundReceive for setting and clearing MDC around receive execution.
* Proper documentation was added for Scala and Java under the Logging/Slf4j section.
