Add the debugging flag.
Add signal handling

Since the hub is a daemon, we need to do something reasonably
intelligent when it receives signals.  This change adds signal
handling: SIGINT and SIGTERM result in a call to stop() (graceful
shutdown); SIGUSR1, if supported, results in a call to shutdown()
(shut down right now).
Pass a list to the HubServer constructor.
Implements the command line processing for the hub

This is the implementation of the command line interface for starting
the HeyU hub.