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/document_loader.rs

@@ -3,7 +3,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 //! Tracking of pending loads in a document.
-//! https://html.spec.whatwg.org/multipage/#the-end
+//!
+//! <https://html.spec.whatwg.org/multipage/#the-end>
 
 use dom::bindings::root::Dom;
 use dom::document::Document;