Fix handling of retained messages with QoS > 0. 

Update ReleaseNotes.md 

Update MQTTnet.nuspec 

Fix build scripts. 

Merge branch 'master' of https://github.com/chkr1011/MQTTnet 

Fix UWP build errors. 

Update project files. 

Improve RPC client handling. 

Added reference to SparkplugNet.