[ci skip] Add a proper to string method and clarify the return type for bulk update

lib/instance.js

@@ -135,6 +135,10 @@ module.exports = (function() {
     }
   });
 
+  Instance.prototype.toString = function () {
+    return '[object SequelizeInstance]';
+  };
+
   /**
    * Get the value of the underlying data value
    *

lib/model.js

@@ -158,6 +158,10 @@ module.exports = (function() {
     }
   })();
 
+  Model.prototype.toString = function () {
+    return '[object SequelizeModel]';
+  };
+
   Model.prototype.init = function(modelManager) {
     var self = this;
 
@@ -1338,7 +1342,8 @@ module.exports = (function() {
   };
 
   /**
-   * Update multiple instances that match the where options.
+   * Update multiple instances that match the where options. The promise returns an array with one or two elements. The first element is always the number
+   * of affected rows, while the second element is the actual affected rows (only supported in postgres with `options.returning` true.)
    *
    * @param  {Object}   attrValueHash                   A hash of fields to change and their new values
    * @param  {Object    where                           Options to describe the scope of the search. Note that these options are not wrapped in a { where: ... } is in find / findAll calls etc. This is probably due to change in 2.0
@@ -1350,7 +1355,7 @@ module.exports = (function() {
    * @param  {Number}   [options.limit]                 How many rows to update (only for mysql and mariadb)
    * @deprecated The syntax is due for change, in order to make `where` more consistent with the rest of the API
    *
-   * @return {Promise}
+   * @return {Promise<Array<affectedCount,affectedRows>>}
    */
   Model.prototype.update = function(attrValueHash, where, options) {
     var self = this;