[REQUEST] Move to Furo, a better Sphinx theme.

[i0bs]

Describe the feature.

While Karma has done a great job for us so far, it's caused numerous issues:

• Lack of theme picker (dark/light)
• Inability to view source code
• Search bar poorly functional with automodule usage
• Current theme has colors uncomfortable to the eye
• Inability to permalink to a method, class or attr
• Cannot preview attr/arg types when hovering (hover refs)

The goal of Furo is to eliminate all of these issues, which you can view an example of here: https://sphinx-themes.org/sample-sites/furo/

Code of Conduct

• I agree to follow the contribution requirements.

[FayeDel]

This is closed because #938 is merged.