Clean up documentation

This website documentation is a bit cumbersome to navigate and find what I'm looking for. It would be great to have the documentation reformatted similar to how readthedocs is done.

Start by reviewing the current website documentation and comparing its navigation with the Read the Docs style requested in the issue. The issue names no files or tests, so first identify the documentation structure and agree on the intended navigation changes. Done means the documentation is reformatted and easier to navigate.

Written by the indexing model from the issue text.