Shadow mapping

[themuffinator]

A simple, working implementation with stencil fallback as an initial goal, build and refine from there.

[themuffinator]

This remains in progress. Current shadowmapping is fairly extensive with primitive transparency handling, CSM and filtering options in place. It currently works well under a variety of conditions, although the following issues prevail:

• despite a strong effort to resolve this, minor peter panning still persists
• complex scenes lack some shadowing, this may necessitate tuning how sky shadows function
• angled/slope projection causing some breakage
• transparency shadowmapping is flat shaded rather than factoring projection of alpha coverage and textures
• transparency shadowmapping lacks filtering