Added an EXIF data field (HTML5 compatible)

I added a new data field (like title and link) so the user can specify EXIF data (things like the camera, focal length, film speed, etc.) using a data-exif attribute in the link. I added some bogus EXIF data to the demo HTML page; it displays in the same color as the number but the same text size as the title. This should make it clear the the EXIF information supports the title but is still more interesting than the number.