Pretty much the last set of changes I'm going to make:

- Make top-left image more friendly to caches by randomising the URL,
  rather than having the URL point to a CGI that returns a random image.
- Change the whole left side bar to use lists for the links, as they should
  be, rather than lines of text seperated by <br>'s.
- Add valid XHTML and CSS logos, because we now comply.