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.
Ah, I guess it depends how one visualises/thinks about programs. I think about it as myself being the CPU and following along the execution i.e. I'm personally inside the scope and so things come to me; while I guess others may think about the CPU/execution being a separate entity so things go to it.