mathfilter 5.x-1.1

I've added image caching to the Mathfilter module, using some suggestions from one of the issues submitted by a user, and so this should greatly improve server performance because you won't need to be serving a cgi for the images every time. Also, page loads will be faster since only small gifs will be returned, rather than waiting for the cgi to create and export the gif. I've recently included an option to do this caching if your Drupal website is behind a proxy server, and your CGI is on the other side of the proxy.

I've also corrected the settings page and reformatted the code to make it easier to read (including adding more comments to the code). This should make it easier for future maintainers.