Some replication architecture planning.

I decided during this that 'view.py' was a bad name, and went with 'replicant.py' instead,
which turned out to be what I was calling the old, WAL-reading approach. So,
I put the WAL approach in an attic along with a note about what was tried and why it didn't work.
New early morning idea: put the streaming of the current and new state together in one subroutine.

Hopefully this makes it easier to match up timelines.
It also cleans up the API: now all is done within a single
standard (if long-running) postgres client session, instead
of circumventing postgres with FIFOs
(though I do like the idea of FIFOs and sockets for flexible IPC)
documentation
Split watch() from its test cases.