Support for XML Namespaces

I'm using Facebook XFBML namespaced tags in my app (e.g. <fb:like>) and Ractive fails to parse them.
http://developers.facebook.com/docs/reference/javascript/FB.XFBML.parse/

So I decided to add ':' as a valid match for such tags (it's still not exact validation, e.g. ':' should not be used at the end of the tag, but at least now parser doesn't fails).

http://www.w3.org/TR/REC-xml-names/#NT-NCName
It's not valid for HTML, but probably for XHTML it is.

You need to decide if you want to support namespaced tags in the Ractive parser.