Listen command

This patch includes a `listen` command along with several command
line switches and associate defaults:
    --hostname      Broker host name (default="localhost")
    --port          Port the broker is listening on (default=5672)
    --exchange      Name of the exchange type (default="amq.direct")
    --routing-key   Routing (binding) key (default="test")
    --username      User name (default="guest")
    --password      Password (default="quest")
    --vhost         Virtual host name (default="/")