Proposed new state facility
A proposal for #1163 (closed).
I haven't updated any of the calling code in tor-hsservice yet. I think the way this will be used ought to be fairly obvious from the API.
This commit also contains a file of notes about stuff I found in an arti state directory. These may be too random even to put in doc/dev/notes, so for now I've put them next to state_dir.rs.