Add reserved? method to detect reserved IP addresses

[collimarco]

trafficstars

This library already has private?, link_local?, loopback?, etc.

It would be useful to have a reserved? method: https://en.wikipedia.org/wiki/Reserved_IP_addresses

One of the reasons would be to mitigate SSRF attacks in a simple way, by limiting connections to "normal" "external" IP addresses (!ipaddr.reserved?).