added load stylesheets by directory feature

I have updated so that you can now pass in ```parker some/directory``` and all .css files will be added. I didn't add support for ```parker directory/*.css``` as omitting the *.css does the same thing anyway. 

This could be updated to accept a wild card or maybe a regex that could be used to work out if the file should be included. Also maybe the ability to include css from nested directories - something like this ```parker directory/**```?