Metadata Refactor
* add MetadataRequest and MetadataResponse namedtuples
* add TopicMetadata namedtuple
* add error codes to Topic and Partition Metadata
* add KafkaClient.send_metadata_request() method
* KafkaProtocol.decode_metadata_response changed to return a
MetadataResponse object so that it is consistent with server api:
[broker_list, topic_list]
* raise server exceptions in load_metadata_for_topics(*topics)
unless topics is null (full refresh)
* Replace non-standard exceptions (LeaderUnavailable,
PartitionUnavailable) with server standard exceptions
(LeaderNotAvailableError, UnknownTopicOrPartitionError)
Conflicts:
kafka/client.py
test/test_client.py
test/test_producer_integration.py
test/test_protocol.py
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