Todo:
   - Complete support for SDL_Mixer groups.
   - Complete support for SDL_Effects.
   - Add sdl_ffmpeg/smpeg module bindings.
   - Rename fsdl module into sdl (required refactoring "load fsdl"
      => "load sdl")
   - Remove static classes used for wrapping; use namespaces if needed
     (required refactoring, search&replace "SDL.", "MIX." etc).

