formating: upgrade to black 20.8b1
This required a couple of small tweaks to un-confuse black, but now it
works. Big formatting changes come from:
* Dramatically improved collection-splitting logic upstream
* Black having a strong (correct IMO) opinion that """ is better than '''
Differential Revision: https://phab.mercurial-scm.org/D9430
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.