Implemented simple Zookeeper support. Using Kazoo.

This was built on top of the gevent patch (#37).

• For Producer, it provides support retries in case there is an error during send
• For SimpleConsumer, it provides support for re-balancing of partitions among other kafka-python clients. (We can look at full support for Java/Scala clients once the new design is finalized). This will allow us to use kafka as a backend for systems like celery.

You can have a look at the code here:
mahendra/kafka-python@gevent...zookeeper

Not tested yet. Will keep updating the code as I progress with the tests.