- parse-atom: 'you' and 'yourself' keywords resolve to (ref <name>) so
they look up the let-binding the tell-command installs.
- 'your <prop>' no longer aliases 'my <prop>' — it's the possessive over
the 'you' binding, mirroring 'its' over 'it'.
Unblocks 'you symbol represents the thing being told' and 'can take a class
and swap it with another via with' (via you/your in tell handlers). Net:
tell 6→7 (was 6/10).