Improve listening usability

Add Listener.register and Listener.run

examples/removebot.py

@@ -1,10 +1,10 @@
 import fbchat
 
 session = fbchat.Session.login("<email>", "<password>")
-
-listener = fbchat.Listener.connect(session, chat_on=False, foreground=False)
+listener = fbchat.Listener(session=session, chat_on=False, foreground=False)
 
 
+@listener.register
 def on_message(event):
     # We can only kick people from group chats, so no need to try if it's a user chat
     if not isinstance(event.thread, fbchat.Group):
@@ -14,6 +14,4 @@ def on_message(event):
         event.thread.remove_participant(event.author.id)
 
 
-for event in listener.listen():
-    if isinstance(event, fbchat.MessageEvent):
-        on_message(event)
+listener.run()