Improve project documentation

[luiscubal]

I am looking into this project since this is something I've wanted for long.
However (and I know this is acceptable since the project is recent), I can't help but notice that xwt is not well documented.
Perhaps this git repository should include a Wiki?

In particular, I am interested in:

1. What are the goals and anti-goals of the project
2. What is the exact expected behavior of TimeoutInvoke in EngineBackend
3. What is the absolute minimum required to have a working backend (e.g. the most important parts)

[slluis]

Thanks for your interest! I'll try to put some basic docs together this weekend.