Add correlation ID for requests and a sequence number for trace output.

[kevinswiber]

This is needed for tracing to determine which trace lines are correlated with the same request and to record the time sequence. Async communication can create a partially ordered queue. These proposed changes will help to resolve ordering by the client.

Example:

{
  "requestId": "9cff0456-84b3-401a-89f6-bc9eae559369",
  "sequenceNumber": 1
}

[kevinswiber]

This change landed in commit 96d9f8b.