Extended streaming API interface maintaining backward compatibility

The Twitter library by [sixohsix](https://github.com/sixohsix/twitter) implements the streams as generators, which is a very intuitive API and much easier to implement than the current one, where you have to subclass the streamer to implement several methods and possibly use queues to communicate between them.

    stream = TwythonStreamer(consumer_key, consumer_secret, oauth_token, oauth_secret).user()
    for tweet in stream:
        # Things and stuff

I originally replaced the old interface, which saves a lot of code, but this version maintains backward compatibility, except that errors are no longer silent by default.