Also adds the incomplete modifier_volume example.
This also adds vec2 for UV coordinates, and obj_to_cpp has been
modified to parse vertex texture coordinates from obj files.
This fully threads both the real minimum size of the texture and the
dimensions of the texture through to the TA parameters.
This also removes spurious zero-area drawing commands (space
characters).
This still needs to be cleaned up, particularly to properly pass the
texture size around--there are a few unnecessary '128x256' magic
numbers scattered in the code.
