Added Multi-state Value object example and unit tests, and added to demo/server example application.
Fixed Analog Input object, Analog Output object, Analog Value object, Device object, Multi-state Input object, Multi-state Output object examples to return correct error codes for WriteProperty service (per BACnet 135.1-2009-9.22.2.6).
Fixed top level ReadProperty and WriteProperty handlers in Device object to return correct error codes (per BACnet 135.1-2009-9.22.2.5)