Basic WebGL with example.

This is a minimal re-factoring of the WebGL library wrapper in order to get a basic example working. I have not checked in dist/builtin.js; you will need to generate the distribution (The generated files cause merge issues and should, perhaps, be excluded from the source).

This is just a beginning. I plan to work on more extensive examples and improving the library. One outstanding question is whether the Python WebGL wrapper should become more object-oriented than the underlying native JavaScript API.