Make MeshBuf capable of handling more arbitrary attributes.
Always use cdraw to render fastmeshes.
Publicized additional stuff from MapMesh.
Make TexSI parent public.
Added a moddable GLSL Value for the object-space vertex position.
Make GLSL mix() available through Cons.
Create a GLSL attribute vertex-array type.

Though it's not practically usable yet, since meshes would need to be
compiled separately for every program they're used with.
Merge branch 'core'