self_test: add dox (also to wiki)
tex_codecs: further work; renamed+reorg for clarity. separating codecs
from IO implementation
This was SVN commit r2654.
tex.cpp now has loader API and codec support routines.
provide for codecs "transforming" the image; this allows e.g.
decompressing DDS, which is currently done in ogl code (but belongs
here)
This was SVN commit r2648.