Remove jsonpickle as part of music21j
Squashed 'src/ext/jsonpickle/' content from commit 76418f7

git-subtree-dir: src/ext/jsonpickle
git-subtree-split: 76418f709dc10099c6db7131fdc936f0c7be1e29
Merge commit '05b35c4cfbea27acb4aa52255f64232d9a329636' as 'src/ext/jsonpickle'