Some small fixes and opinionated changes

Some where discussed on the mailing list here:
https://groups.google.com/a/opentechschool.org/d/topic/coaches.python/_NqvlkYl5hs/discussion

The diff is short, straightforward and speaks for itself.

Here are the compiled changes:

http://sonoflilit.github.io/python-beginners/en/getting_started.html#running-python-files
http://sonoflilit.github.io/python-beginners/en/simple_drawing.html#drawing-a-square
http://sonoflilit.github.io/python-beginners/en/functions.html