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.

sky = 20, 23, 24
border = 20, 23, 24
water-top = 21, 57, 76
water-bottom = 21, 57, 76
water-opacity = $80
music = snow.ogg
clouds = 4