Added SDL_mixer and TODO list

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Added SDL_endian

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Made some stuff in SDL_mixer more idiomatic

Signed-off-by: Jacky Boen <aqiank@gmail.com>
Fixed some syntax errors

Signed-off-by: Jacky Boen <aqiank@gmail.com>