Generate bindings for HTMLMeterElement.
Remove more unnecessary lists of imports.
Generate bindings for HTMLModElement.
Generate bindings for HTMLObjectElement.
Generate bindings for HTMLOptGroupElement.
Generate bindings for HTMLOptionElement.
Generate bindings for HTMLOutputElement.
Generate bindings for HTMLParamElement.
Generate bindings for HTMLSelectElement.
Generate bindings for HTMLUnknownElement.
Generate bindings for Comment and DocumentType.
auto merge of #817 : jdm/servo/optgroupelem, r=kmcallister

Also remove all traces of the non-element Node bindings! Woo!