Eliminate the requirement that TMeshCache's gpu_data_type have a null value
Define OpenGL::MeshCache, a TMeshCache implementation for OpenGL-based rendering that uploads mesh data to GL buffers.
Remove render-to-texture for the time being. No implementations currently exist so I can do this with impunity
Fix spelling; plural of "vertex" is "verticies".
Clarify meaning of desired_quality, remove out_realquality parameter, and add overloaded function which supports listeners.
Add ICamera parameter to ISceneRenderer::set_scene_root to specify which camera to render from.
Rebase OpenGL::RenderBase on top of ISceneRenderer.
Add render_node method for subclasses to use.

Add protected constructor and pure virtual destructor.
Define OpenGL::DeferredRenderer, a RenderBase implementation that draws entire scene into a "G-Buffer" FBO, then does lighting as a post-process operation.
Coding standards: fix indentation