Holidays need duration

[okhowang]

In some country, holiday may last several days, for example china spring festival, korea lunar new year.
in #63, three holidays are defined. BeforeLunarNewYear/LunarNewYear/AfterLunarNewYear.
If holiday has duration, it can be more graceful

[rickar]

Agreed. It may require a special flag to mark extended holidays so the existing logic is kept simple.