Closes #182

* Improve the documentation, especially in describing how to PUT and
  PATCH to list configuration subresources.
* Improve the return codes for many error corner cases.  Specifically,
  this makes more consistent when a 400 error is returned or a 404 error
  is returned.
* Improve the handling of some weird corner cases, and add tests.
* Fix the setting of error response reasons by not trying to .format()
  into a bytes object (which isn't allowed in Python 3).
* Add lots of comments to the code, which improves the readability of
  all the twisty little turns.
* 100% code coverage for listconf.py!