Add ilamb3 API documentation

[nocollier]

While not pertinent to the current effort, we will soon want entire API documentation for the ilamb3 project. I have loosely followed numpydoc rules throughout but I am sure that an automated tool will find that many of the docstrings are lacking.

• Which tool do we integrate with myst to do the generation?
• Create a page that will link to the index page.
• Cleanup docstrings.

I also think this is a good moment to add flags/notes to functions we aren't sure we need or that might be good to revamp/revisit.