Added a hook for creating Elements, and allowed hooks to be passed arbitrary data.
Made s.addAll, which is the old s.add.  Made s.add only take a single item, so we can focus on it and add arbitrary metadata which plugins can hook on to.  Made ID plugin do this!
Made the hook name format `${type}.${event}` for scalability.
Added class plugin.
Made class plugin add s.hasClass, s.addClass, s.removeClass, and s.toggleClass.