audio: add cutmp3

cutmp3 is a small and fast command line MP3 editor. It lets you select
sections of an MP3 interactively or via a timetable and save them to separate
files without quality loss. It uses mpg123 for playback and works with VBR
files and even with files bigger than 2GB. Other features are configurable
silence seeking and ID3 tag seeking, which are useful for concatenated mp3s.

(nia)