discovered that above mentionend functions are a bit outdated.
ogg2mp3 doesn't work as advertised on my system, maybe lame changed behaviour ?
the archive functions don't know about xz and the simple-extractor can generally
use some overhowl.

beside fixing the above, I rewrote simple-extractor so that:
* it behaves consistently for all archive types (no more deleting of source file
or not depending on archive type e.g. .gz vs .tar.gz)
* it takes filepaths as well as URIs
* it handles more archive types
* it optionally deletes the source archive