Add option to include own interface IP and MAC address in output

[royhills]

Add --includeself (-c) option to include our own interface IPv4 and MAC address in the output.

The IP address shown will be the first address on the interface.

Issue: #40

[coveralls]

Coverage: 91.13% (-0.2%) from 91.296% when pulling e1e60d8 on display-own-addresses into fe2b609 on master.

[royhills]

I think the best way to implement this will be to create the ARP packet structures for a fictitious ARP response packet appearing to come from the host's own interface IP/MAC then call display_packet() in the same way that the pcap callback function does for a real response.