Release 3.4.0-beta.1

• Updated and rewrote Notification 2.0 listener implementation. Added additional parameters for more control:
  consumer_name, shared, auto_ack and auto_unsubscribe. Added unsubscribe function for removing
  subscribers on demand. Both AsyncListener and Listener now provide consistent start/stop functions
  which take care of coroutine and thread creation. The listen function can still be invoked directly if
  necessary.