to the shelf script approach.

Factored out some functions in ldraw.py so they can be used in both
approaches.

Realized that the post-compensation in xform is just the inverted
initial matrix, so bake that in before setting node/point xforms.

Fetch the color_lib() at the module level. Might not be the best idea
but easy for now.

Lacking some features in the HDA and the build_model_points path in
general. We should still expose all the LDraw Part options (gaps etc.)
and store material paths on prims. I probably missed some other bits
too.

Added HDA for procedurally loading entire ldraw files, as an alternative