Code style and doc improvements

Finally, we have the perfect score.

Global evaluation
-----------------
Your code has been rated at 10.00/10 (previous run: 10.00/10, +0.00)

Lets keep it this way!

If you disagree with pylint (and you may be right!) use:

# pylint: disable:pylint-code-of-the-error

It is up to the reviewer to decide whether it is appropriate.