Free OpenGL textures used by sprites

[tung]

Sprites use OpenGL textures, but never free them, which might cause problems if lots of sprites are loaded and used. Sprites should free their textures when garbage collected.

[tung]

This is best done in the OpenGL library itself, by treating textures as userdata and attaching an appropriate __gc metamethod. The current pre-compiled ones don't do this, so it'll need to be added and then rebuilt.

[tung]

Refactor sprite.lua to use new sdlgl.texture.

• Closed by cc52392.