Fix tests.
Diary entry.
Fix NACKs.
NACK testing.
Merge branch `rewrite` into `master`.
Add callbacks.

Need to use step for some tests.
Begin using step().
Working on callbacks.
Test sendPrevious().
Create 'nack.t.js'.
Work on NACK test.
Diary entry.
Fix nack test.
Fix prepare phases.
Update nack test to use prepare phase callback.
Diary entry.
Merge branch `rewrite` into `master`.