Generate bindings for Node, CharacterData, Text, Element, and HTMLElement. Hook up text nodes to use the new bindings.
Generate bindings for HTMLHeadElement.
Generate HTMLHtmlElement bindings.
Generate bindings for HTMLAnchorElement.
auto merge of #674 : jdm/servo/nodegen, r=kmcallister

The first commit sets up a bunch of the infrastructure required and gets Text nodes onto the generated bindings. The remaining commits generate bindings for and convert selected element types to use them. The last one (HTMLAnchorElement) should be representative of the kind of work required for remaining elements, I've worked out and minimized the repetitive goop that's required.