Use Sphinx to generate API docs

[lbalmaceda]

Changes

Sphinx was set up with an old version which was completely broken. This PR does:

• Update Sphinx to the latest version, re-running the quickstart.
• Use the read-the-docs theme
• Fix the content to be displayed, both at the home page and sidebar of the generated documentation.
• Update the README headers, reorganizing sections into a more readable doc.
• Git-Ignore the generated docs, as those will be generated and hosted by https://readthedocs.com/.

The docs are generated by changing the directory into /docs and running make html.

The resulting index page will display the README contents first and on the sidebar the API docs.

How to review this PR

Is better to clone the PR, generate the docs, and open the resulting index.html file.

References

• https://docs.readthedocs.io/en/stable/intro/getting-started-with-sphinx.html
• https://www.sphinx-doc.org/en/master/usage/extensions/autodoc.html
• https://samnicholls.net/2016/06/15/how-to-sphinx-readthedocs/
• https://sphinx-rtd-tutorial.readthedocs.io/en/latest/build-the-docs.html

[jtemporal]

👏 🎉 LGTM