reformat codebase using python/black

[dneise]

I open this PR just to see if the test are still running after reformatting using python/black

[dneise]

Since black does not exist for Py2, I first decided to verify codestyle only on Py3 (after all the style check is Py version independent). But having conditional steps turned out to be rather hard.

In the end I thought:

Why not define one dedicated job for all style checks?

So now the Style checks are run using py3.7 and for all other Pythons we skip the style checks and only build and run the test suite.

[cclauss]

plug ins for many editors

[cclauss]

Also "plugins" is a single word (no space).

[dneise]

Thanks - done

[dneise]

@cclauss and @StoicLoofah could this be merged?

[StoicLoofah]

sorry for being delinquent on merging the other branches, but there are now conflicts to resolve here. @dneise can you take a look at those?

Regarding the discussion on documenting and enforcing black, this is exactly what i was hoping for. thanks for integrating those!

... now i need to get black setup myself =)

[cclauss]

The precommit hook is the way to go... It blackens the code in the commit process.

[dneise]

@StoicLoofah ok, I think this can be merged now

[dneise]

@StoicLoofah

I am sorry, this PR has a bit of an ugly commit history. Maybe you could to a squash + merge commit? in order to have a cleaner history?

After all, the only thing I did in this PR was black . and then figure out how to verify blackness on circleci.

[StoicLoofah]

Looks great! Good suggestion on the squash.