Implements new properties and methods

[DZamataev]

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.

These improvements need more testing though.

[DZamataev]

Ok, I did it.