Websocket support

Referencing #26
Actually I've done some work on implementing websocket in mochiweb. It's based on misultin websocket implementation and mochiweb_http module.
We've been using it on production for over 2 years (as library for comet server) on Brainly group websites and it performs quite well with traffic up to 40k concurrent users.

I just added tests, example of usage and documentation. I'm aware that there is still need to do some work on this module so I look forward for feedback. :)