A simpler kafka consumer

```
kafka = KafkaConsumer('topic1')
for m in kafka:
    print m

kafka = KafkaConsumer('topic1', 'topic2',
                      group_id='my_consumer_group',
                      auto_commit_enable=True,
                      auto_commit_interval_ms=30 * 1000,
                      auto_offset_reset='smallest')

for m in kafka:
    process_message(m)
    kafka.task_done(m)
```
I think we need a function in common which looks like so:

    def binary_string(s):
        if isinstance(s, six.binary_type):
            return s
        if isinstance(s, six.string_types):
            return s.encode('utf-8')
        raise KafkaParameterError(s)