Updated Jamendo plugin audioformat and listformat descriptors. Attempted to
use v3.0 API for playlist tracks. Still no playlist API endpoint. So using
a separate track requests now.
Implemented a new action/playlist_convert URL extractor, which shall
henceforth be known as "jamj" (JamJibberish).
Fixed XML url extraction in regex mode, trivial backslash deescaping for JSON
formats; and fixed multiply URL bug by copying row{} dict during conversion.