Add IP range / CIDR utilities to libphutil
- In the long run, I want to allow authentication artifacts to be restricted to specific IP ranges (for example, a bot's Conduit token might only work if the bot is on the corporate network).
- Right now, I want to require HTTPS only for calls from outside the Phacility network. Calls between boxes get to use HTTP so we don't have to deal with the SSL for now / maybe ever.
Test Plan: Wrote a pile of test coverage.
Reviewed By: btrahan
Differential Revision: https://secure.phabricator.com/D11043