Ownership guide

This is a work in progress, but this should get *extensive* review, so I'm putting it up early and often.

This is the start of a draft of the new 'ownership guide,' which explains ownership, borrowing, etc. I'm feeling better about this framing than last time's, but we'll see.
Ahhh, so this ties into the 'lifetime' vs 'scope' thing, I think. I prefer "where does it say" to subtly reinfore that this isn't a time-based thing, it's a static thing. But yeah, I sitll like the wording.