Add scripts:
fix-deutex-pngs - Apply the output of deutex to the build
map-color-index - Map from one color index to another
Script fix-deutex-pngs is to standardize PNGs by applying the result of
the expanding IWADs produced with deutex to the build. It is invoked by
build target fix-deutex-pngs
Script map-color-index can map from one color index to another. Most
likely it will be used to map form legacy transparency 255 to similar
color 133, which can be done by build target
fix-legacy-transparency-pngs.
