we right-justifiy binary data text to max 76 chars (min 16) per line
similarly to the way the stdlib plistlib module does (although they
use tabs for indentation, equivalent to 8-spaces).
We write the plist doctype ourselves, otherwise lxml always adds a
newline to it (even wen pretty_print is False).
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.
