Adapt CSS from processing.org site #2

Right now, there is no styling associated with any pages in the reference—there's a link to a stylesheet in the header, but the link doesn't go anywhere. We've been directed to "simply to use the same CSS (more-or-less) as the main Processing Reference, with some changes to the fonts and colors. No need to be creative" (according to golan).

I interpret this to mean: we should make a copy of the existing CSS file on processing.org, cut out anything that doesn't look useful, and make some modifications to what remains to give it a more distinctive look.

This will presumably involve modifying the HTML templates a little bit, or adding a directory of static files that need to be included when building the site.