A GL Hello World.

Demonstrates how to use Bro to bind the OpenGLES library well enough to compile
a shader program, upload some vertex data and draw it.

I'll eventually "enable" more of the GLES2 bindings, but I want to do that in a
context where they're getting tested.
Fixed headers.
Merge pull request #12 from samskivert/hello-gl

A GL Hello World.