Fix commonmark Markdown warnings in docs, part 1

Fixes warnings from rust-lang/rust#44229 when `--enable-commonmark` is
passed to rustdoc.

This is mostly a global find-and-replace for bare URIs on lines by
themselves in doc comments.

components/script/dom/htmlmetaelement.rs

@@ -135,7 +135,7 @@ impl HTMLMetaElement {
         }
     }
 
-    /// https://html.spec.whatwg.org/multipage/#meta-referrer
+    /// <https://html.spec.whatwg.org/multipage/#meta-referrer>
     fn apply_referrer(&self) {
         if let Some(parent) = self.upcast::<Node>().GetParentElement() {
             if let Some(head) = parent.downcast::<HTMLHeadElement>() {