and tell coverage to don't include __init__.py

Have the pool call a wrapper, dispatch_worker_thread, that runs in
the new thread. The wrapper catches all exceptions, logs a backtrace,
then re-raises the exception.

GH: closes #17

GH: closes #55

Thanks teor and juga for feedback!

GH: closes #57

Closes #59

Oops.

- Default config needs a nickname to pass validation
- It doesn't need to be set in init.py because it doesn't depend on
  anything at runt ime. So just ...
- Set it in config.example.ini so it ends up in the client's new
  config.ini