Excluse some CSS files

[jfgoncalves]

It would be nice to be able to exclude some CSS files, like Foundation files, because we just need to check our custom .css and not the Foundation ones, and it really takes place for nothing.

[geuis]

I think having a way to avoid stylesheets is good. I don't know how when I'll have time to work it. Feel free to fork the code and try adding the feature.

[Anahkiasen]

+1 for this