added deck.chat modules

deck/chat.py

@@ -23,7 +23,9 @@ class DeckChat:
   def command(self, command, handler):
     """
     Register a new handler inside the chat instance.
-    The handler accepts a single parameter, which is the state object.
+    The handler accepts two parameters: a message and a state object,
+    and returns the response and the new state object.
+    Non-command handler is registered under the 'default' command.
     """
     cmd = command.strip().lower()
     if cmd.startswith(self.command_prefix):