Another omnibus PR

There's a few bugfixes and performance improvements here:

* Sped up message decoding by no doing operations like ``crc32``
  * Some are more useful than other and this will probably get refined in the future. I was just trying a lot of different things to speed consumers.
* A bunch of logging around bad offset recovery, but haven't been able to track down the source of the problem.
* Handle the case where a message is larger than the default fetch size. [Fixes #102]
* Convert all configuration to kwarg parameters with default values [Fixes #45]

This code has been running in production for almost 3 months for us, so I'm confident in the changes.