set method support set object value by path

[Javey]

The set method should support set object type value by path like bellow:

this.set({'a.b': 1, 'a.c': '2'}, {path: true});
// trigger $change:a.b $change:a.c $change:a $change $changed:a.b $changed:a.c $changed:a $changed
this.get('a') // {b: 1, c: '2'}

[Javey]

The behavior is default, pass path: true is unnecessary.

this.set({'a.b': 1, 'a.c': '2'});
// trigger $change:a.b $change:a.c $change:a $change $changed:a.b $changed:a.c $changed:a $changed
this.get('a') // {b: 1, c: '2'}