Add/update comments with links to spec

Extracted out of #5649

* add more hyperlinks to associated specification for structs/methods
* follow redirects and update links
* replace broken links
* removal of WHATWG multipage page name since the page name is not
  guaranteed to be stable

components/script/dom/domimplementation.rs

@@ -25,6 +25,7 @@ use util::str::DOMString;
 
 use std::borrow::ToOwned;
 
+// https://dom.spec.whatwg.org/#domimplementation
 #[dom_struct]
 pub struct DOMImplementation {
     reflector_: Reflector,