Write new pxfmt_decompress_pixels() to "fetch" 1 pixel at a time.
Removed old pxfmt_decompress_pixels()
Start plumbing for S3TC/DXT1 instead of ETC1.
Starting to port relevant portion of Mesa3D's DXT1 wrapper.

This is the "fetch" (i.e. decompress a block and give 1 texel) code.  I need to
get code that's equivalent to Mesa3D's code for opening and dynamically linking
from a shared library.
Hacked in some S3TC/DXT support, using the Mesa3D-external lib.

I pulled pieces of the following Mesa3D files, and hacked on it a bit to not be
dependant on the Mesa3D code base (and to fit more of the style of code within
VOGL):

- src/mesa/main/texcompress_s3tc.c
- src/mesa/main/dlopen.h