Implements new properties and methods

Thanks for the awesome work! This parser helped me a lot. Let me introduce some improvements.

Implements methods to get ```index``` and ```parent``` of the node. Pretty basic but needed in many scenarios.
Implements ```removeChildAtIndex:``` which is useful when you have ```index``` of element.
Implements ```removeAttributeForName``` which is also very useful when dealing with HTML, clearing page, for example.