added RWops functions (well, some of them)

SDL_audio.h: Not started yet
SDL_image.h: Added only IMG_Load_RW
SDL_mixer.h: Not started yet
SDL_rwops.h: Missing SDL_RWFromFP and SDL_AllocRW.
SDL_sound.h: Not started yet
SDL_ttf.h: Not started yet
SDL_video.h: Not started yet