Support Xpath features

[hominee]

I am fan of xpath when parsing and extracting data from html file.
Currently, dyer do not support html paring, you have to implement the parser on your own.
I am considering add a xpath feature to the response for better integration with C library libxml2.

[hominee]

The first version of XPath feature is out in commit ,
its underlay library is rust binding of C libxml2.
More can do to strip the dependencies since dyer only parse the HTML, In order to do that I intend to bind C libxml2 with rust in an organized manner what the ongoing repo is aimed at.