TEXMAP addition to Official Library Spec

[Orion Pobursky]

Based on the above discussion, I change my proposal to the following:

!TEXMAP Meta
Sufficient !TEXMAP <geometry2> and/or <geometry3> lines (as outlined in the Texture Mapping (!TEXMAP) Language Extension) must be included such that the part renders correctly in non-!TEXMAP supporting programs. It is highly encouraged that the included geometry reflect the pattern created by the !TEXMAP, even if it is reduced in resolution or colors, but this is not required.

In addition, the spec should be further clarified as discussed above.