add a Python Interface for IrssiNotifier

While irssi itself loves Perl, Python is quite a nice language too.
People even might want to send notifications from Python because
  * they use weechat instead of irssi (traitors)
  * they use X-Chat instead of irssi (even bigger traitors)
  * want to abuse the nice interface IrssiNotifier offers for other
    notifications coming from their machines (regular hackers)
  * they execute Python via exec in irssi because they can

For all these people, let there be a Python interface:
    >>> notifier = IrssiNotifier(API_KEY, PASSWORD)
    >>> notifier.send_message("message", "#channel", "nick")