Implement `img::load_img` (`IMG_Load` from `SDL_image`).

Because life without transparent images is so boring...
Mac framework support
Merge pull request #30 from pcwalton/mac-framework

Mac framework support
Merge pull request #29 from dpc/upstream

Implement `img::load_img` (`IMG_Load` from `SDL_image`).
Made SDL image optional
Merge branch 'mixer' of git://github.com/pcwalton/rust-sdl into pcwalton-mixer

Conflicts:
	Makefile.in
	ll.rs
	sdl.rc
Added a basic readme file.
Corrected some styling issues in README markdown, and clarified flags
usage
Add mixer::allocate_channels, mixer::query, and mixer::playing