Documentation review

[frostedoyster]

Attempt to update and clean up the documentation.
Preview: https://sphericart--143.org.readthedocs.build/en/143/

[github-actions]

Here is a pre-built version of the code in this pull request: wheels.zip, you can install it locally by unzipping wheels.zip and using pip to install the file matching your system

[frostedoyster]

I haven't touched the CUDA C++ and torch docs yet. I think we should wait for CUDA C++ to match the C++ API and for #141 to be merged. Everything else should be ready

EDIT: updated CUDA C++ docs

[ceriottm]

The CUDA c++ example seems to imply that there is just compute, but the API also specify compute_with_gradient and compute_with_hessian - I suspect it needs updating.