Unity Sprite Atlas Compression
http://forum.unity3d.com/threads/2d-sprite-packer-and-pvrtc.218633/
http://docs.unity3d.com/Manual/SpritePacker.html
http://docs.unity3d.com/Manual/class-TextureImporter.html
http://docs.unity3d.com/ScriptReference/Sprites.AtlasSettings-compressionQuality.html
http://docs.unity3d.com/ScriptReference/Sprites.AtlasSettings.html