https://github.com/fonttools/ufoLib2/blob/master/src/ufoLib2/plistlib.py
replaces the old ufoLib.plistlib shim, privides a single interface
similar to python3's stdlib `plistlib` module, but built on top of
lxml.
On python < 3, it requires the singledispatch backport.
This will be added as conditional installation requirement.