Add Actor API and improve debug log output

emper/Actor.hpp

emper/Blockable.hpp

emper/Debug.cpp

emper/Debug.hpp

emper/Dispatcher.hpp

emper/Runtime.cpp

emper/Runtime.hpp

emper/Scheduler.hpp

emper/UnboundedBlockingMpscQueue.hpp

emper/lib/adt/MultiList_UnboundedWaitFreeMpScQueue.hpp

emper/strategies/laws/LawsScheduler.cpp

emper/strategies/ws/WsScheduler.cpp

tests/CMakeLists.txt

tests/SimpleActorTest.cpp