Simple utility class for calculating Christian holidays

From time to time I still get questions about some post I did several years ago on eksperten.dk. As there's no license in the post, people are worried if they can use the code. Of course they can. Here it is.

Example of usage:

var thisYearsEaster = new HolidayCalculator().CalculateEasterSunday(DateTime.Now.Year);

var nextYearWhitSunday = new HolidayCalculator().GetWhitSunday(DateTime.Now.AddYears(1).Year);

The calculations for the most common (european) Christian holidays are defined. PR's are welcome if you miss some.