Async wrapper: you need to import handlers separately.

TIL.
Set logger level properly
postSomething: return decoded JSON if possible

I'm not sure how it worked before, but now the json conversion is
explicit. Unfortunately error messages are not served over JSON.
Async wrapper: more logging fixes.
Async wrapper: refactor waitings

Now the backoff is handled more consistently without as many
hardcoded constants.

Findings:

* If you don't wait between messages, you get rapidly increasing
  backoff every 2nd message; how rapid depends on your backoff
  multiplier.
* If you wait 5 seconds between messages, you get reasonable backoff
  (still every 2nd message)
* If you wait 7 seconds between messages, you get no backoff at all
  and you can post as much as you want.