* Basic RTT support in the works. Bind new Buffer2D<T> depth and
  color buffers with RT_BindBuffers() and the default framebuffer(s)
  with RT_BindDefaultBuffers()
* Due to the generalization of framebuffers and depth buffer,
  the default framebuffer now points directly to vram.
* Deleted old DrawTriangles() rasterizer. Code was not used.