Added RenderOperations and a rendering test

RenderOperation (a container class for vertex array objects, vertex
buffer objects, and element array objects) has been added. They
automatically split into an appropriate number of streaming and static
VBOs.

The algorhithm currently does not support translucent objects
(transparent texels are discarded in the shader). I'm too lazy to fix
this, as it would require separating opaque polygons from translucent
polygons. Also, it would result is performance hits (increased Shader
and Texture state changes). Maybe someday.