Canteen/CanteenHTML5 — pull request #7 by JustBlackBird (2014-12-25 14:30:11+00:00)
Title: Add iframe to specification

According to [this](http://www.w3.org/TR/html5/embedded-content-0.html#the-iframe-element) `iframe` is a valid HTML5 tag. At the same moment there was no `iframe` tag in `\Canteen\HTML5\Specification` class.

This PR adds the `iframe` tag support.