Use code formatter

We should stop to take care manually of the code format.
I mean locally, we could set this up in the CI but I don't like the idea to change the code after push.

I'm used to black, a part of the code is already made using it. There's also autopep8, or yapf I don't know if one of these allow to autoformat only selected text.

I love black, except for the fact it will add one line for each function arg or dict element, if it cannot be kept in a single line, with respect to --max-line-length.

What do you think ?