Add linter to Github actions

[mre]

Description

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Issues Fixed or Closed by This PR

• Add linting to the build process. See use python 3.6 typing #33.

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[cmangla]

@mre Wow this is turning out to be a lot of work, but looks great!

[mre]

@cmangla, yeah let's take it as an opportunity to clean up non-idiomatic code.
I think the result is great: 6e48d48
If we all fix a few of those lints from time to time, we'll be in a much better position soon.

[mre]

Of course, after pylint, we still have mypy to tackle. And who knows what else. 😆