Just a friendly suggestion for Andy.
I would add "upgrade" instructions to the overview page. One thing worth mentioning in there would be for anyone that has altered the holiday.php file, that they should NOT
upload a fresh copy of that file with any future upgrades as it would remove any changes they made.
I made a few changes to my holiday.php file like adding Easter, first day of spring, first day of summer, first day of autumn and first day of winter and I also added the daylight savings start & stop days.
Still lovin' this add on! Keep up the great work Andy!