Concordance register.py

I have the main Python callback in Concordance working now to handle <iq/>, <message/>, and <presence/> elements. Eventually it'll only handle these elements when they're directed to the server, otherwise the server will route the message to it's destination without Python needing to process it first.

examples/register.py demonstrates user registration handling using ElementTree (or at least the start of the process for now). The result is shown here.