WARNING: needs manual upgrade
fix: make cover and song paths relative

Upgrade Instructions:
- shutdown the server
- update the git repo
- make a backup of songs.db
- edit songs.db, replacing all occurrences of your music_dir and all
  parts where it refers to the "<path_to_git_repo>/dbs/covers/". This
  can be performed in vim with the `:%s^<music_dir_here>^^gc` and
  `:%s^<path_to_git_repo>/dbs/covers/^^gc`
- start the server up again and you should be all good!