Set up Sphinx autodoc for prediction and interface code

[isms]

Overview

When docs are built (e.g. with make html run from docs directory), the prediction and interface projects should have their docstrings converted to entries in the documentation.

Technical details

• Add one code.rst document that has its contents derived automatically from docstrings — don't worry about breaking this up into smaller files yet
• Add the new document to the main toctree (table of contents) in index.rst
• Important note: this project's chosen convention is to use Google-style docstrings rather than Sphinx style

Out of scope

You don't need to add to or fix existing docstrings as long as there is at least one that shows the autodoc is working.

Acceptance criteria

• Docs build correctly with make html run from docs directory
• Syntactically correct Google-style docstrings in prediction and interface pieces of the project can get built using autodoc when the appropriate entry is put into code.rst
• At least one autodoc entry in code.rst demonstrates this is working

NOTE: All PRs must follow the standard PR checklist.