tested locally with `pylint --rcfile=pylint.rc -E kafka test`. should
pass travis builds.

Initial support for consumer coordinator

Use unblocking io for broker aware requests

Consumers get_messages: allow blocking until some messages are received

Fix translation of Java murmur2 code, fix byte encoding for Python 3.

Reworked the if statement logic to only call stop() on not-stopped producer objects

Allow null payload for deletion feature