aiokafka 0.3.0

Major docs upgrade. Many consumer fixes including new API's.

on Python PyPI

Starting from 0.3.0 we discourage imports from kafka namespace. Starting from 0.4.0 aiokafka will stop supporting objects imported from kafka namespace. Please import from aiokafka namespaces instead.

• Moved all public structures and errors to aiokafka namespace. You will no
  longer need to import from kafka namespace.
• Changed ConsumerRebalanceListener to support either function or coroutine
  for on_partitions_assigned and on_partitions_revoked callbacks. (PR #190
  by @ask)
• Added support for offsets_for_times, beginning_offsets, end_offsets
  API's. (issue #164)
• Coordinator requests are now sent using a separate socket. Fixes slow commit
  issue. (issuer #137, issue #128)
• Added seek_to_end, seek_to_beginning API's. (issue #154)
• Updated documentation to provide more useful usage guide on both Consumer and
  Producer interface.