Add Git ignore file.
Add details to the readme file.
Add ALTTP resources.

- Musics: all of them should be here.
- Sounds: all ALTTP sounds used in ZSDX are here.
- Sprites: all ALTTP sprites used in ZSDX are here.
- Tilesets: only the light world tileset of ZSDX is here. I will only
  add dungeon tilesets in the v1.3 branch because they will use string
  tile pattern ids.