TextureCompiler: Add ARGB Support

[lonestalker]

dxt3 support especially...
for some more advanced core game mods...

[MWisBest]

Unless I'm missing something here, it seems like it already supports DXT3.
ARGB support is now on the To-Do list! 👍

[lonestalker]

http://i.imgur.com/C2UbUHG.png < screen shot of the errir
https://www.dropbox.com/s/8fdlp2cdfcbvll2/trackmapstest.rar?dl=0 < .rar with all the textures
it wont let several dxt 3 textures work.

if you could get these textures working then trackmaps for all the unused tracks could be added without issue + lots of other things could be added.

currently since you cant import these dxt 3 textures you have to import them as dxt1 or dxt5 which causes huge graphical glitches basically rendering the whole addition a waste.