Add pylint to tox.ini; test both kafka and test; default to error-checking only; fixup errors; skip kafka/queue.py
Raise TypeError in kafka.producer.send_messages if any msg is not a str (or subclass); document
Add producer unit test (test/test_producer.py); check supported types in send_messages
Merge pull request #211 from dpkp/str_only_produce_msgs

Strictly enforce str message type in producer.send_messages
Merge pull request #208 from dpkp/add_pylint_to_tox_ini

Use PyLint for static error checking
Improve leader failover tests; note that async produce failover is broken -- so skip that test for now
Add warnings to README, docstring, and logging that async producer does not retry failed messages