Add reserved? method to detect reserved IP addresses

[collimarco]

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?).

[collimarco]

Elixir already has a module for this: https://hexdocs.pm/safeurl/SafeURL.html

[taketo1113]

@collimarco

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

In this use case, it is not possible to make a strict determination based on whether the address is reserved, so it might be better to have a method that determines whether an address is globally reachable. What do you think?
#68 (comment)

Also, are there any other real-world use cases where reserved? would apply?