Discard cruft.

Discard cruft upon realization that not only has the wheel already been
invented, but it's actually already pretty good too.

The ZMTP/1.0 implementation is still clever, so that's probably still a
problem.
Add tests for the ZMTP/1.0 framing.

There were tests before, but they were bundled into the old
sender.go/sender_test.go.  These new tests are less comprehensive but
they're a start.
Merge remote-tracking branch 'github/master'
Update README.md.