Xtra Tunes: A Vanilla Music Pack

Additions:
- New disc textures added for the following: creator, creator music box, precipice, relic & tears

Changes:
- readme.txt renamed to changelog.txt
- Version coding redone to differentiate away from Minecraft's version coding (aka just removing the '1')
- Sound files renamed to exclude descriptor letters at the front of their names
- File structure redone to match Minecraft's sound files
    File structure now as following:
        - menu music in music/menu/
        - nether music in music/nether/
        - end music in music/end/
        - overworld music in music/game/
        - disc music in music/records/
    All other music files are in the music folder normally.