Changelog entry for Message API.
## ChangeLog
+### New Features
+
+* Added support for
+ [`MessageProducerSegment`](https://godoc.org/github.com/newrelic/go-agent#MessageProducerSegment)
+ to be used to track time spent adding messages to queuing systems like
+ RabbitMQ or Kafka.
+
+ ```go
+ seg := &newrelic.MessageProducerSegment{
+ StartTime: newrelic.StartSegmentNow(txn),
+ Library: "RabbitMQ",
+ DestinationType: newrelic.MessageExchange,
+ DestinationName: "myExchange",
+ }
+ // add message to queue here
+ seg.End()
+ ```
+
+* Added new attribute constants for use with message consumer transactions.
+ These attributes can be used to add more detail to a transaction that tracks
+ time spent consuming a message off a queuing system like RabbitMQ or Kafka.
+ They can be added using
+ [`txn.AddAttribute`](https://godoc.org/github.com/newrelic/go-agent#Transaction).
+
+ ```go
+ // The routing key of the consumed message.
+ txn.AddAttribute(newrelic.AttributeMessageRoutingKey, "myRoutingKey")
+ // The name of the queue the message was consumed from.
+ txn.AddAttribute(newrelic.AttributeMessageQueueName, "myQueueName")
+ // The type of exchange used for the consumed message (direct, fanout,
+ // topic, or headers).
+ txn.AddAttribute(newrelic.AttributeMessageExchangeType, "myExchangeType")
+ // The callback queue used in RPC configurations.
+ txn.AddAttribute(newrelic.AttributeMessageReplyTo, "myReplyTo")
+ // The application-generated identifier used in RPC configurations.
+ txn.AddAttribute(newrelic.AttributeMessageCorrelationID, "myCorrelationID")
+ ```
+
+ It is recommended that at most one message is consumed per transaction.
+
* Added support for [Go 1.13's Error wrapping](https://golang.org/doc/go1.13#error_wrapping).
`Transaction.NoticeError` now uses [Unwrap](https://golang.org/pkg/errors/#Unwrap)
recursively to identify the error's cause (the deepest wrapped error) when generating
