Generate docs using Doxygen to Sphinx via Breathe (rtd theme)

[kenorb]

Refs:

• https://github.com/doxygen/doxygen
• https://breathe.readthedocs.io/en/latest/
• https://github.com/sphinx-doc/sphinx
• https://github.com/readthedocs/sphinx_rtd_theme
• https://sphinx-rtd-theme.readthedocs.io/en/stable/installing.html
• https://samnicholls.net/2016/06/15/how-to-sphinx-readthedocs/
• https://docs.readthedocs.io/en/stable/intro/getting-started-with-sphinx.html
• https://www.star.bnl.gov/public/comp/sofi/doxygen/config.html#cfg_file_patterns

[biohazardxxx]

Just want to emphasize this how great this would be. A browsable documentation would help a lot to use the framework at other projects. 👍

[kenorb]

Related PRs:

• GH-521
• GH-567