Unified Event System

[Kudu]

I suggest adding a unified event system to BBot. The interface could be something like this:

class Module(object):
    def on(self, *args):
    """
    .. :py:method:: on(events, handler)
                    on(events, selector, handler)

        Attach an event handler function to one or more events, optionally limited by a selector.
        An event could be an IRC command name (like ``"NICK"``), an IRC command numeric string (like ``400``) or an abstract event (like ``"LEAVE"``).
        The selection passes if the "main data" (such as the text for a message) is either equal to the selector or if ``selector.match(data)`` is ``True``.
        When an event is matched and the selection passes, the handler is called with a Message object as its argument.

        :param events: the events to handle
        :param selector: the selectors
        :param handler: the handler function
        :type handler: :py:class:`~types.FunctionType`
    """

I apologize in advance if the reST isn't very good.