JSdoc fixes

Ad:
 -  update is alias for updateAll.
 -  Make callback optional for save method

lib/persisted-model.js

@@ -243,6 +243,9 @@ PersistedModel.updateAll = function updateAll(where, data, cb) {
   throwNotAttached(this.modelName, 'updateAll');
 };
 
+/**
+ * Alias for updateAll.
+ */
 PersistedModel.update = PersistedModel.updateAll;
 
 /**
@@ -284,7 +287,7 @@ PersistedModel.count = function (where, cb) {
  * @options {Object} [options] See below.
  * @property {Boolean} validate
  * @property {Boolean} throws
- * @param {Function} callback Callback function called with (err, obj).
+ * @param {Function} [callback] Callback function called with (err, obj).
  */
 
 PersistedModel.prototype.save = function (options, callback) {