Use black pep8 codestyle

@GregAshton another change I'd like to do on my own fork: use 'black' code formatter, which I'm a fan of to fully get rid of formatting-style ambiguities resulting in uniform-looking code.

[this should be merged only after the previous one !19 (merged) as it sits on top of it]

see https://black.readthedocs.io/en/stable/