Add document.title

Wanted to play around with your codebase a bit; thought I should make myself useful.

Wasn't sure if I need to follow the [SVG instructions](https://html.spec.whatwg.org/multipage/dom.html#document.title), also node.namespaceURI was only on the root (not the children), so that needs to happen first anyway.
[Step 3](https://html.spec.whatwg.org/multipage/dom.html#dom-tree-accessors:strip-and-collapse-whitespace) seems to be missing here.