docs($location): document $location's events

Closes angular#1569
Closes angular#4446

src/ng/location.js

@@ -525,6 +525,35 @@ function $LocationProvider(){
       return html5Mode;
     }
   };
+
+  /**
+   * @ngdoc event
+   * @name ng.$location#$locationChangeStart
+   * @eventOf ng.$location
+   * @eventType broadcast on root scope
+   * @description
+   * Broadcasted before a URL will change. This change can be prevented by calling
+   * `preventDefault` method of the event. See {@link ng.$rootScope.Scope#$on} for more
+   * details about event object. Upon successful change
+   * {@link ng.$location#$locationChangeSuccess $locationChangeSuccess} is fired.
+   *
+   * @param {Object} angularEvent Synthetic event object.
+   * @param {string} newUrl New URL
+   * @param {string=} oldUrl URL that was before it was changed.
+   */
+
+  /**
+   * @ngdoc event
+   * @name ng.$location#$locationChangeSuccess
+   * @eventOf ng.$location
+   * @eventType broadcast on root scope
+   * @description
+   * Broadcasted after a URL was changed. 
+   *
+   * @param {Object} angularEvent Synthetic event object.
+   * @param {string} newUrl New URL
+   * @param {string=} oldUrl URL that was before it was changed.
+   */
 
   this.$get = ['$rootScope', '$browser', '$sniffer', '$rootElement',
       function( $rootScope,   $browser,   $sniffer,   $rootElement) {