Improve find method

[valentindusollier]

Hi,

Thank you for your library 😉

In one of my projects, I had to find nodes by their name and some of their attributes. So I implemented it:

xmlQuery(ast).find('body', {'type': 'text'}); // xmlQuery containing all the body elements which has a 'type' attribute of value 'text'

And I think it would be a good feature for this lib.