Implement hva parser.
Add renderer support for matrix uniforms.
Add a Vertex ctor with z-pos.
Add renderer support for toggling the depth buffer.
Add voxel renderer.

Only supports the Gl renderer (needs Cg shaders).
Add sequences equivalent for voxels.
Add a widget for UI voxels (e.g. colorpicker).
Initial implementation of RenderVoxel* traits.