Refactored the zeroless module and changed its API significantly.
Topics for the pubsub pattern were introduced, as zmq 3.0 onwards
implements filtering at the publisher side. As a result of that,
topics were worked out, in order to make the pubsub pattern less
prone to user mistakes. Also, the replacement of the old logic in
favour of coroutines, improves zeroless performance for long
running applications.
Updated tests to comply with the zeroless module new API. Also,
made fixtures names clearer.
Made the topic part of the pubsub message, even when none was set.
Updated all examples to comply with the zeroless module new API.
Updated the README file to comply with the zeroless module new API.
Increased minor version in the setup.py file.
Merge pull request #13 from x8lucas8x/revampAPI

Revamped the zeroless module api.