Documentation Overhaul

Created by: fsoubelet

PR for #263 (closed). Major changes include:

• New landing page, now including the OMC logo
• New CSS theme
• Additional documentation in various places
• Full consistency over all docstrings (module & function)
• New index structure
• New doc structure
• Makefile target for documentation build
• A few additional type hints

Easiest way to understand the changes would be to checkout this branch, run make doc and navigate the pages. Feedback welcome!