* Rework texture build system to be automatic:

	For shareware build, extract a list of textures used in the 
	shareware wad levels. Build the shareware wad containing only
	these textures.

	For the full build, include all textures.

	This removes the need to fiddle the textures around whenever a 
	new wad is added to the shareware build and also should make
	the wad more compact.

* Make textures be in alphabetical order.

* Split up sprites so their offsets are stored with the image files.
