Add additional hooks for callers:

* Resolve relative URLs.
* Set priority on any stylesheet implementation.
* Substitute content during XML Conduit traversal in place of computed styles.

Update Stylish HTML Conduit to use fixed psuedoelement handling.

Add support for ::before/::after psuedoclasses to HTML Conduit bindings.

Parse HTML 'style' attributes.

Have Stylish HTML Conduit depend on a non-buggy version of Stylish Haskell.

Draft html-conduit to Stylish Haskell bindings.

Initialize stylish-html-conduit sidemodule.