Moves most of the code relating to YCoCg and Alpha Exponent into
misc.c/h, in the interest of making the rest of the codebase cleaner.
Removes the decode option from the import menu, as encoded files are
always decoded now (there used to be a menu button for doing this
after import, but with it gone there's no reason ever to not decode).
Finally, the remaining functions in color.c were only ever called once,
so these were extracted and inlined, and the empty file deleted.
Fixes two major issues with mipmap generation, namely sRGB transforms
being applied both backwards and in 8-bit precision, causing severe
color degradation. sRGB transforms are now handled correctly and all
mipmap generation is done at 32-bit floating-point precision.
A new cubic filter has also been added (Catmull-Rom) which rounds-out
the existing lineup of cubic filters.
Also includes extensive code cleanup (sorry I couldn't separate this)
to mipmap.c/h and color.c/h
Stayd