URL/UDPv6 support for the UDP sender.

URL/UDPv6 support for the UDP sender.

This adds support for URL strings to support IPv4/IPv6 addresses, hostnames,
and optional port numbers to the UDP sender. The syntax is based on RFC 3986,
example URL strings to be used with the 'add'/'delete' commands are:

    	10.10.1.2:8000		# host:port
    	10.10.1.2		# host with default port 8000
    	localhost		# hostname (for IPv4 or IPv6 host)
    	localhost:8001		# hostname with port
    	[::1]:8000 		# same, but different syntax
    	[badc0de::1]		# IPv6 host with default port 8000

The 'delete' command now also supports port-wildcarding, i.e. not specifying
the port in the 'delete' command removes all targets whose host names match.

The UDP sender has been tested to function with IPv6, including multicasting:
 * server: para_server --udp_target=[ff05::beef]:8000 --udp_mcast_iface=eth1
 * client: para_audiod -F -D -r 'ogg:udp -i ff05::beef -I eth0'