anchor.diff:      chroma = enableAcoustid;
       convert = enableConvert;
       discogs = enableDiscogs;
  -    echonest = enableEchonest;
       embyupdate = enableEmbyupdate;
       fetchart = enableFetchart;
       lastgenre = enableLastfm;
  
positive.code: , enableBadfiles       ? true, flac ? null, mp3val ? null
  , enableConvert        ? true, ffmpeg ? null
  , enableDiscogs        ? true
  , enableEchonest       ? true
  , enableEmbyupdate     ? true
  , enableFetchart       ? true
  , enableLastfm         ? true
  
negative.code:                                    pythonPackages.requests2
      ++ optional enableConvert      ffmpeg
      ++ optional enableDiscogs      pythonPackages.discogs_client
      ++ optional enableLastfm       pythonPackages.pylast
      ++ optional enableMpd          pythonPackages.mpd
      ++ optional enableThumbnails   pythonPackages.pyxdg
  