Add the Shared Address Space

[cesine]

Summary

https://tools.ietf.org/html/rfc6598

Shared Address Space is distinct from RFC 1918 private address space
because it is intended for use on Service Provider networks.
However, it may be used in a manner similar to RFC 1918 private
address space on routing equipment that is able to do address
translation across router interfaces when the addresses are identical
on two different interfaces. Details are provided in the text of
this document.

This document details the allocation of an additional special-use
IPv4 address block and updates RFC 5735.

The Shared Address Space address range is 100.64.0.0/10.

Why

We use ip and recently started using the shared ip range for some of our servers, which meant that some of our requests were being flagged as public. We added the isShared function so that we can also use that in our business logic.