Setup a CSS test suite

[jaytaph]

There are a few things we like to do:

1. • download real world CSS stylesheets (top 1000 websites for instance)
2. • benchmark processing of these stylesheets
3. • return stats on css properties: which ones do we support, which are the most used ones etc..

This could help us in the benchmarks to see improvements (or not) of the CSS system, and we can find the properties most used so we can focus on those to be implemented first.