Test example code

[lorey]

If the code changes, examples break. Maybe there's a way to test example code easily during automated testing.

Found solutions:

• https://www.sphinx-doc.org/en/master/usage/extensions/doctest.html
• https://thomas-cokelaer.info/tutorials/sphinx/doctest.html
• https://gist.github.com/twidi/9ce8ed0e8f92788031daaa78a765da75

[lorey]

Code can be included within .rst, maybe just run the code and include it.

[leo8198]

I created a #28 pull request to address this issue. I'm not using sphinx because I think that pytest solves the problem for now.