Also more docs

fix docs: iter_messages doesn't (any longer?) take a FetchRequest 

...it takes the same args and instantiates its own one

Ref #8

Creates a producer process and one consumer process per partition. Uses
`multiprocessing.Queue` for communication between the parent process and
the producer/consumers.

```python
kafka = KafkaClient("localhost", 9092)
q = KafkaQueue(kafka, client="test-queue", partitions=[0,1])
q.put("test")
q.get()
q.close()
kafka.close()
```

Ref #8

Fixes #2