twisted_ari: Create initial file structure

For an initial project structure, I'm going to go with:
 * events.py - manage the websocket/events.
 * ari.py - manage HTTP requests.
 * twisted_ari.py - public front end.

Where all the information gets tied together is still a bit unknown, but
keeping these three things separate feels like a good start.
README: Note what we use for our style guide
events.py: Add WebSocket client

Add the Autobahn WebSocket client. This defers most of its work to some other
resource, to be added later.