Add support for Cisco wildcard masks

[troglobit]

Jerry Przybylski writes:

At our house, for our gig-fiber service, we use a Cisco 2921 router instead of a consumer-grade router. The documentation of the Cisco IOS "standard" Access-Control statements uses xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy syntax where x is the network, and y is the COMPLEMENT of the usual netmask. A /24 network in an ACL would be 0.0.0.255 instead of 255.255.255.0

It would be nice, I think, for netcalc to support (output only, or output and input) this alternate (mask-complement) net-mask syntax too.

I agree, this would be a neat thing to add to netcalc. Very neat and tidy first task for someone new to the project :)

For more information, e.g., see https://en.wikipedia.org/wiki/Wildcard_mask