Add an iso/checksum update utility script.

[kentfredric]

This utility script does some basic HTTP requests/result parsing and updates the ISO datestamp and checksum to the latest values available from the gentoo distfiles mirror.

It uses features ( state ) and dependencies ( JSON::PP, HTTP::Tiny ) that have been available in stock Perl installations since before 5.14.0

You may of course want to implement the same functionality in some other language, but my proficiency in perl made it a more natural choice for a proof-of-concept, and I will be understanding if you don't wish to merge it =).