librdkafka v1.4.4

v1.4.4 is a maintenance release with the following fixes and enhancements:

• Transactional producer could crash on request timeout due to dereferencing
  NULL pointer of non-existent response object.
• Mark rd_kafka_send_offsets_to_transaction() CONCURRENT_TRANSACTION (et.al)
  errors as retriable.
• Fix crash on transactional coordinator FindCoordinator request failure.
• Minimize broker re-connect delay when broker's connection is needed to
  send requests.
• socket.timeout.ms was ignored when transactional.id was set.
• Added RTT/delay simulation to mock brokers.

Note: there was no v1.4.3 librdkafka release