I made two proposed changes to the section about programming style:

1) The `pep8` application for checking your code is no longer maintained. The most recent version is now called `pycodestyle` to avoid confusion with the name of the standard itself. This PR fixes this.

2) I thought the mention of the alternative Google style guidelines was sort of confusing (which I do not believe to be a strict superset of PEP8). So I tried to make the language a bit clearer that there are just multiple standards that one could choose to follow.