* Allow for UDP servers
Extend the Server interface with ServePacket and ListenPacket - this is
in the same vein as the net package.
Plumb the packetconn through the start and restart phases.
Rename RestartPair to RestartTriple as it now also contains a Packet.
Not that these can now be nil, so we need to check for that when
restarting.
* Update the documentation
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