MDAnalysis formatting with black

[RMeli]

Hello MDAnalysis developers!

As you might have noticed from recent PRs, we are in the process of formatting the whole MDAnalysis code base with black.

This process should not affect open (and active) PRs, thanks to the work done by @marinegor in #4815.

If you are going to work on new features, please make sure you are working with the latest version of the develop branch. This will avoid many possible conflicts when opening a new PR.

If you already started working on an older version of the develop branch and have issues or concerns on how to bring your own development branch up-to-date, please feel free to contact/tag me (@RMeli), and I'll be happy to help to get things sorted.

Best,
Rocco

[RMeli]

With #4885, the formatting process is almost over! 🚀

Only the files touched by recent PRs are not formatted, and have been explicitly excluded in #4815. They will be formatted on a case-by-case basis (when the related PR is merged).

#4886 will exclude the formatting PRs from git-blame.