Docgen using Sphinx with Bazel

The sphinxdocs project allows using Bazel to run Sphinx to generate documentation. It comes with:

• Rules for running Sphinx

• Rules for generating documentation for Starlark code.

• A Sphinx plugin for documenting Starlark and Bazel objects.

• Rules for readthedocs build integration.

While it is primarily oriented towards docgen for Starlark code, the core of it is agnostic as to what is being documented.