major facelift: -!-> and -?-> appear

- rename projects to akka-channels and akka-channels-tests
- move implementation into akka.channels.macros package
- remove picking up ActorRef as sender (or none at all)
- factor out logic to make different façades acting upon Future[] or Any
  so that -!-> and -?-> can complement the traditional <-!- and <-?-
- the new operators are easily distinguishable from !/? and the
  rightwards-pointing go with the flow and compose better, let’s try
  them out