Light sources

[dany-on-demand]

The engine should support light sources at some point. Needs #166

[iamgreaser]

It should support shaders first.

[iamgreaser]

Yes, that's right, this is all OpenGL 1.1 + GL_ARB_vertex_buffer_object. Thus, we have no shaders.

I'll be fine with adding GL 2.1 shaders, but will need to work out the best approach for it, and will also have to stab people who make shaders that only works on their GPU.