Add sphinx for documentation

[tkilias]

Background

• Sphinx is a standard documentation system for python https://www.sphinx-doc.org/en/master/
• It provides documentation generation from reStructuredText or markdown
• It can generate menus
• It can generate api documentation from python docstrings
• It can generate documentation for Readthedocs https://readthedocs.org/

Acceptance Criteria

• - Have a working setup for sphinx with api documentation generation
• - Additional contents:
• - Installation, Usage, Developer Guide
• - CI tasks which generates the documentation
• - Optional: get it published on github pages

[redcatbear]

@tkilias, please provide description.