docs: use a separate page for each term

[josharian]

Instead of a giant docs page with everything on it, switch to a page per term (scope, modifier, etc.).

Then we can add more rich content about the term, including examples, metadata, language applicability, etc.

[pokey]

This issue is a subset of #867, but prob not a bad idea it to have its own focused issue. That issue is more of a brainstorm in issue form 😅