allow specifying a single port, fixes #4

[bronson]

Tested both syntaxes on my server, everything seems to work.

[bronson]

here's an example from my server's config:

        "port_map": {
            "udp": [53],
            "tcp": [53, 25, 587, 993, 80, 443]
        }

vs

        "port_map": {
            "udp": [[53, 53]],
            "tcp": [[53, 53],
                    [25, 25],
                    [587, 587],
                    [993, 993],
                    [80, 80],
                    [443, 443]]
        }

[saschpe]

Nice one