Using constructor chaining in AcknowledgedBulkWriteResult
Removed BulkWriteError base class.  Changed BulkWriteItemError to BulkWriteError.
Renamed BulkWriteConcernError to WriteConcernError
Renamed UpdateRequestBuilder to BulkUpdateRequestBuilder, WriteRequestBuilder to BulkWriteRequestBuilder, and BulkWriteOperationBuilder to BulkWriteOperation