Transmoogrification - Moose => Moo conversion of HTTP::Throwable

Hello Ricardo,

This patchset switches HTTP::Throwable from Moose to Moo-based.  It passes all of the current tests, and I've also tested it with the Moose-based subclassing in timbunce/WebAPI-DBIC.  I've added dependecies on Type::Tiny, Types::Standard, Package::Variant, and namespace::clean.  Please let me know if there's anything you would like me to change or fix.  Thank you and have a great day!

Cheers,
Fitz