Linting

[egpbos]

Following #41 and #93, we should set up linters.

In the tox suite, we already run flake8. However, the configuration is not picked up automatically when running flake8 separately, which is annoying, because then the settings are not picked up by my editor. We should put the configuration somewhere standard where it is picked up.

After that, we could also look into pylint in strict mode and see what that turns up.