Limit SQS message pulls to 10

* Bug reproduced by having a prefetch_multiplier and process
  count that multiply together to become greater than 10. This bug
  is on a per worker basis, and not a per instance basis.
* Fix: Anything greater than 10 gets floored to 10.
* Efficient work around this hard cap: Decrease process count per worker
  and add a new worker. Set process count and prefetch multiplier such that
  they multiply to 10.
Adds Eric Reynolds to AUTHORS
Cosmetics for #291
Expose redis error types as get_redis_error_classes()