Changes between 5.8.0 and 5.9.0.RC1

This is a pre-release for 5.9.0, a maintenance release with a new feature, a bug fix, and dependency upgrades. All users of the 5.x.x series are encouraged to test this version.

Allow configurable correlation ID generation in RpcClient

GitHub issue: #637

Make sure qos, heartbeat, max channel are unsigned shorts

GitHub issue: #642

Bump optional dependencies

GitHub issue: #644