Modernize the look of our generated docs

[JOJ0]

The readthedocs theme we are using, in my opinion, looks and feels outdated. I'm currently reading a lot of data science and machine learning related documentation. The PyData theme for Sphinx seems to be very popular and I have to admit that I like it very much. Have a look at these random docs links which use that theme :

• https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.columns.html
• https://matplotlib.org/stable/gallery/style_sheets/style_sheets_reference.html
• https://scikit-learn.org/stable/modules/generated/sklearn.cluster.KMeans.html#sklearn.cluster.KMeans

BTW I also would have experience in implementing the PyData theme, since I did it for the Beets project already (https://beets.rtfd.io).

Nevertheless I'd like to start a discussion on what theme would be best for the synadm project. Some more suggestions I like are:

• The "Book" theme: https://sphinx-themes.org/sample-sites/sphinx-book-theme/ - pretty similar to PyData but feels slightly more minimalistic. Actually I prefer it over PyData at the moment!
• The "Insegel" theme: https://sphinx-themes.org/sample-sites/insegel/
• The "Awesome" theme: https://sphinx-themes.org/sample-sites/sphinxawesome-theme/

Here's an overview of (all?) available Sphinx themes - but be aware of that not every theme has the same features when it comes to usability: https://sphinx-themes.org/