WIP
Check if a date is a german holiday (nation-wide or in a specific state). This is currently nowhere near complete. And yes, I know that I've gotten myself into an impossibly large rabbit-hole.
Hoping for the best the API is supposed to look like this. Check the tests to see how that's turning it out.
let newYears = DateComponents(calendar: .init(identifier: .gregorian),
year: 2020,
month: 1,
day: 1)
newYears.date!.isGermanFederalHoliday // true
newYears.date!.isGermanHoliday(in: .sn) // true