Command line tool to convert audio files to mp3 based on gstreamer.

There are many tools available, but I was not able to find one
with the following features:
   - batch conversion of directories
   - handles all input files (using gstreamer plug-ins)
   - mp3 input files are just copied, not re-encoded
   - if the output file exists, it is skipped

It has a uniq naming convention for the output file
- the ouput file is named after the title of the song with all
  unicode characters decomposed and normalized (for example a
  u-umlaut "ü" becomes a simple "u"), and all potential 
  non-compatilbe characters stripped.
- to allow several versions of the same song, a hash of the album,
  track and title is added to the file name
- the file is placed in a directory named after the artist with
  all sanitation mentioned for the song title