Translate CSS Selectors to XPath Expressions

 Translates a CSS3 selector into an equivalent XPath
 expression. This allows one to use CSS selectors when working with
 the XML package as it can only evaluate XPath expressions. Also
 provided are convenience functions useful for using CSS selectors on
 XML nodes. This package is a port of the Python package 'cssselect'
 (<https://cssselect.readthedocs.io/>).