Refactored TTexture to allow encoding sprite(s) at an arbitrary location within
a (possibly shared) physical texture.
The original variant only allowed encoding a sprite at the bottomleft of a
larger physical texture to use NPOT sprites on POT only supporting systems.
af4dc03dd60d
Make sky, horizon, flakes and clouds optional, replace repeated strips of skyL/skyR with 2x2 transparent PNGs instead of larger images of variable dimensions, remove a number of empty unused images
