Add a username argument to the Token and IceServer calls.

Awesome work on this project so far!

I've been writing a WebRTC sample app against XSClient, and I noticed that a username argument is required for the getWebSocket and getIceServer calls. For some reason this information is missing from the API docs (http://xirsys.com/api/), but the official Ruby and PHP demo apps show this argument being used.

I found that unless I included a username in my getToken calls, I would be assigned an empty id upon connecting to the XirSys signalling server.