UDP support

[ghost]

The system should include support for UDP.

The SimpleSgsProtocol? had the maximum messsage length set to 8032 bytes in preparation for the max UDP packet size (and max message size set to 8000). This was removed because it broke our example code and we didn't have utilities to help users fragment large messages.

At [3987] we bumped the max messages size and payload length back up to be closer to what they were before, to avoid potential incompatibilities (given that we don't have fragmentation utilities).