Add the plugin to our set of listeners for each message that it
        listens to, tell it to use our messages Queue for communication, and
        start it up.

def register(self, plugin):
        """Add the plugin to our set of listeners for each message that it
        listens to, tell it to use our messages Queue for communication, and
        start it up.
        """
        for listener in plugin.listeners:
            self.listeners[listener].add(plugin)
        self.plugins.add(plugin)
        plugin.messenger = self.messages
        plugin.start()