Adopt a code style convention

[EiffL]

Since we are basing the code on TensorFlow, I suggest we follow the Google/TensorFlow code styling for python.

Here are some links to the documentation for this:

• https://www.tensorflow.org/community/contribute/code_style
• https://github.com/google/styleguide/blob/gh-pages/pyguide.md

Essentially, the idea is that we are following pep8, but we only use 2 space tabs instead of 4.

I'll add a github action to run yapf on the code to make sure it is correctly formatted, will also add a pre-commit hook so that yapf can be run automatically before each commit.

[EiffL]

Still interested in feedback from @andrevitorelli and @sfarrens for this :-)