A bit more functionality, still buggy

To wit: multi-part section bodies are getting truncated.
The implementation of the `Docs` nonterminal is TERRIBLE.
Playing whack-a-mole with this bug

Choose one: either you can parse multiple fact docs from a single file
or you can have multiple lines in a fact doc section (e.g., "Caveats:").

I'll probably re-write the BNF more carefully now to see if that helps.