MYST3: TinyGL Renderer

This PR contains an implementation of the software renderer that runs for the engine Myst3.
The renderer shows pretty much the same result as the openGL one, except for the resolution of textures.
ie. tinyGL doesn't support textures larger than 256x256.
tglDepthMask does not seem to function properly. You can test it by loading this savegame http://zmvnbnp41c.piecejointe.net/. There should be no rendering artefacts.