Initial commit.
Add transaction and acknowledged send support.
Tests and fixes for acking.
Implement most of web service.
Remove multi-tuple transactions in place of single-tuple reservations.

I realised that sharded multi-tuple transactions would not work without
*serious* coordination between nodes. By restricting reservations to a
single tuple, the semantics are *much* simpler.
Make reservations work.
Significantly simplify entry management. Add benchmarks.
Use single tuples in service rather than arrays.
Eradicate tuple acks.

It made reasoning about reads/takes/reservations more difficult than it
should be.
Take is always in a reservation. Added ReadAll() and SendMany().
Moved matcher to github.com/alecthomas/expr.