Major improvements --> New version

This version contains several improvements and new features:

* improvement: use genre from discogs as the genre (configurable, so that you are still
               able to use style like in previous versions)
* improvement: provide the picture type "cover image" for flac as well
* improvement: add discogs_id as a tag to each file (as discogs_id for flac and mp3),
               some taggers (e.g. puddletag) need this information
* improvement: add some translations for german umlauts
* feature: add possiblity to provide a separate destination directory (-d)
* feature: add possiblity to provide the release id via a file in the source
           directory. The name of the file as well as the name of the used key
           is configurable, a default configuration is provided
* feature: add possibility to use lower case file and directory names via config option
* feature: add possibility to keep already existing tags in the file (e.g. freedb_id)

I would be very happy, if these changes are merged into the master branch. If not, fine for me as well ;-)