Compatibility

• Fix for python 3.7 support: remove 'async' keyword from SimpleProducer (dpkp #1454)

Client

• Improve BrokerConnection initialization time (romulorosa #1475)
• Ignore MetadataResponses with empty broker list (dpkp #1506)
• Improve connection handling when bootstrap list is invalid (dpkp #1507)

Consumer

• Check for immediate failure when looking up coordinator in heartbeat thread (dpkp #1457)

Core / Protocol

• Always acquire client lock before coordinator lock to avoid deadlocks (dpkp #1464)
• Added AlterConfigs and DescribeConfigs apis (StephenSorriaux #1472)
• Fix CreatePartitionsRequest_v0 (StephenSorriaux #1469)
• Add codec validators to record parser and builder for all formats (tvoinarovskyi #1447)
• Fix MemoryRecord bugs re error handling and add test coverage (tvoinarovskyi #1448)
• Force lz4 to disable Kafka-unsupported block linking when encoding (mnito #1476)
• Stop shadowing ConnectionError (jeffwidman #1492)

Documentation

• Document methods that return None (jeffwidman #1504)
• Minor doc capitalization cleanup (jeffwidman)
• Adds add_callback/add_errback example to docs (Berkodev #1441)
• Fix KafkaConsumer docstring for request_timeout_ms default (dpkp #1459)

Test Infrastructure

• Skip flakey SimpleProducer test (dpkp)
• Fix skipped integration tests if KAFKA_VERSION unset (dpkp #1453)

Logging / Error Messages

• Stop using deprecated log.warn() (jeffwidman)
• Change levels for some heartbeat thread logging (dpkp #1456)
• Log Heartbeat thread start / close for debugging (dpkp)