update.txt

To update for a new Unicode version:
* Update all files in unicode-data/. The sources are given in unicode-data/source.txt. Don't forget to update that file, too, add the modifications to UnicodeData, and create RelatedChars.
* If there are new or updated ranges with an algorithmically defined NAME, update the function nameFallback in js/unicode.js.
* Add the new version to the list on the "About" page in index.html.
* Add a new class for that version to style.css, update the colors for the other classes to look nice.