H: Set ('+') or unset ('-') the given attributes for all audio files matching
H: pattern. Example:
H:
-H: sa rock+ punk+ classic- '*foo.mp3'
+H: setatt rock+ punk+ classic- '*foo.mp3'
H:
H: sets the 'rock' and the 'punk' attribute but unsets the 'classic'
H: attribute of all files ending with 'foo.mp3'.