def subscriber(address,topics,callback,message_type):
return Subscriber(address,topics,callback,message_type)<EOL>
Creates a subscriber binding to the given address and 
subscribe the given topics.
The callback is invoked for every message received.

    Args:
        - address: the address to bind the PUB socket to.
        - topics: the topics to subscribe
        - callback: the callback to invoke for every message. Must accept 2 variables - topic and message
        - message_type: the type of message to receive