docs: switch themes?

[tdegeus]

I'm not a fan of the current doc theme, as it does not provide sufficient outline sidebars. Moreover, it does not have a dark theme. Personally, I've grown to like https://github.com/pradyunsg/furo

[MiWeiss]

Sure, I don't mind :-)

I don't know readthedocs / sphinx particularly well, thus any effort from you in that direction is highly appreciated and will be merged without hesitation :-P

[MiWeiss]

p.s. If you need me to add you as a maintainer on readthedocs, just post your corresponding login-email here and I'll give you the permissions

[tdegeus]

I'm "tdegeus" at readthedocs

[MiWeiss]

I'm "tdegeus" at readthedocs

added :-)