Mojo JS Bindings: Update User's Guide, examples

examples/js/world.js

 #!mojo:js_content_handler
 // See hello.js.
 define("main", [
   "console",
   "mojo/services/public/js/application",
-], function(console, appModule) {
+], function(console, application) {
 
-  class World extends appModule.Application {
+  var Application = application.Application;
+
+  class World extends Application {
     initialize(args) {
       console.log(this.url + ": World");
       this.quit();
     }
   }
 
   return World;
 });