Make provision for passing custom serialisers in woof producer

[sudev]

This patch will help anyone to write custom de-serialisation/serialisation protocols and produce binary data to Kafka.

Say you want to deal with msg pack and not UTF-8.

# Producer 
producer = KafkaProducer(value_serializer=msgpack.dumps)
producer.send('msgpack-topic', {'key': 'value'})

# Consumer 
consumer = KafkaConsumer(value_deserializer=msgpack.unpackb)
for msg in consumer:
     do_something(msg) # here msg is de-serialised to python data structures.

FYI - We wrote make_safe earlier to stop anyone from producing non utf-8 string, now we will keep this as default but will allow anyone to override it.

[ashu-]

👍