Fix warnings in sphinx and enforce tox to fail on warnings

[AurelienJaquier]

In ecode ascii art, use `` to convert ascii into string literal and prevent sphinx to fail on it.

In sAHP, for some reason, I had to remove some | characters to prevent sphinx to fail, even though it was between ``.

Fix code blocks in docstrings.

Modified conf.py so that tox would fail on sphinx warnings, so that we could fix them and keep a full documentation.

For some reason, sometimes the documentation displays the string .. code-block:: python and sometimes it does not. I could not find the reason behind it, but it is a minor issue that I will graciously ignore.

[anilbey]

Great, thanks

Modified conf.py so that tox would fail on sphinx warnings, so that we could fix them and keep a full documentation.

Cool 🚀

[darshanmandge]

thank you!