Html5 audio and video tag

support for the HTML5 audio and video tag. Pull-request created to track progress.
`value` needs to be sanitized before passing it here. If I'm reading this correctly, this bypasses the URI filter completely (e.g. `<video src="http://evil.com/indentify">` would be replaced with `<video src="http://evil.com/indentify?noprogress&max-size=0">`).