Speedup with lxml and tinycss+cssselect

Not sure if this is an interest to you.  Our `pynliner` calls were taking ~30s to execute (complex css from boostrap and others).  I replaced beautiful soup with `lxml` and mostly substituted `cssutils` for a combination of [tinycss](http://pythonhosted.org/tinycss/) and [cssselect](http://pythonhosted.org/cssselect/).  All of which have C modules for speedup.  The end result is inlining goes down to about 5 seconds for a 6X improvement.

The code would need some real cleanup, it's mostly just substituting lines with different library calls right now.  If you think there's a benefit to try to merge this, let's talk.  Otherwise, no problem, I'll just keep maintaining this fork for our specific use.