Update babl.doap and AUTHORS

Make babl.doap compliant to the new DOAP file style (GUADEC 2014):
* Add new mandatory fields 'description' and 'programming-language'.
* Add field 'category'

Add bug tracker URL.
Update mailing list adress.
Remove trailing white spaces.
Add me to AUTHORS.
Fix DOAP file

Remove category.
Remove M4 programming language, because we don't develop with it
(only the Autotools use it internally).
DOAP file: add Ruby programming language.
Remove extra programming languages from the doap file.