Allow for namespaced inky tags

[cumuru]

Would be great to allow XML-namespaced inky tags for integration with templating engines and CMS. Some templating engines like TYPO3.Fluid or phptal are XML-based. Using namespaces would ease both validation and separation, e.g. <inky:container> etc.
I‘m aware of reaching beyond Foundation for Emails compatibility and that this can be resolved with either subclassing or using component factories as well. So this is more like a poll if there are people around interested in improved XML support.