Update CSS from upstream

This pulls in the newest CSS files:
poole/poole:  public/syntax.css  -> pygments.css
poole/poole:  public/poole.css   -> poole.css
poole/lanyon: public/lanyon.css -> lanyon.css

I also made a note of the changes that I made to the CSS files. Those
changes come from my personal fork of Lanyon and I've retained them -
only the new content from the upstream CSS files has been added.