Asyncstompization and de-geventification!

The usual things (remove monkey patches, import from asyncstomp, etc.), plus
replacement of an Event with a Promise in the mail classes.
Fix "syncstomp" references in tests
Use EventPump and cotest in the tests (and alphabetize)
Make update_promise.fulfill consistent across classes
Use get_promise_value from asyncstomp
Update for refactored get_promise_value
Some further copromises and yields
Small cleanup to tests

Using test_010_ instead test_a_ for consistency with other tests (and because
numbers are a better idea anyway); and restoring a couple of placeholder tests
that got deleted because their comments referred to gevent, but which should
indeed still get written.
Merge pull request #2 from LuminosoInsight/asyncstomp

Asyncstomp