Handle the "do nothing" cases.
Fix signed / unsigned mismatch.
Clean up initialization order.
Fix SDL_Color init.
Clean up cruft.
Clean up unused vars.
Ignore build-* directories.

Cherry-picked from "cmake" branch 3d1e4d1.
Import SDL_mixer VS2010 project file.
Adjust source and output paths.
Disable MIDI and FLAC.

These should be uncommon enough we can omit them and save a little
space.
Disable MP3 support.

Some Linux distros do not include MP3-related packages in their core
repos for licensing reasons, so we'll just use Ogg Vorbis instead.
Fix output file suffix and include paths.
Apply disabled settings to other configs.
Add SDL2_mixer project.
Add build instructions.
Add prebuilt SDL_mixer binaries.

Built from SDL_mixer 2.0.0-668.
Import SDL_mixer header.

From SDL_mixer 2.0.0-668.
Fix camelCase in cfg_ui_t.

Fixes #230.
Remove unused WITH_SDL define.
Link with SDL_mixer 2.x.