Slope Meta Command

[Orion Pobursky]

We will be introducing a second color like parameter which only applies a subset of the normal LDraw color material (bumpiness etc can be defined using the !COLOUR meta) in a machine state way.

This is what I want to avoid since the bumpiness, roughness, etc. is independent of color. We'd have to define a new default color that had bumpiness, roughness, etc. That would break every current LDraw program. A !SURFACE meta would just be ignored by renderers that don't support it.