basic aiokafka producers
doc strings for producers
clean up producer tests
Fix trove classifieers
cleanup rpoducers api; add codec constants
add instalation of python-snappy to travis.yml
Merge pull request #2 from jettify/feature-aio-producers

Feature aio producers
Drop code constants from AIOProducer, rename send_messages() to send(), export client and producers in __init__.py
Make flags keywork-only
Add aiokafka.connect coroutine