Docs: Move the documentation to the shared CCPBioSim Sphinx theme #481

What needs to change

Move the CodeEntropy docs from Furo to the shared ccpbiosim-sphinx-theme.

Why

So the CodeEntropy docs match ccpbiosim.org and the rest of the CCPBioSim software, and pick up theme updates automatically.

Suggested changes

• Replace furo with ccpbiosim-sphinx-theme>=1.0,<2.0 in the docs dependencies.
• Set the theme in docs/conf.py.
• Add the banner, quick start and section cards to docs/index.rst.
• Switch the API reference to sphinx-autoapi