Perform basic anniversary calculations
getYears : Time.Zone -> Time.Posix -> DayMonthYear -> Basics.Int
Calculates the number of anniversary years passed
isDay : Time.Zone -> Time.Posix -> DayMonth a -> Basics.Bool
Returns a Bool on whether or not the provided Time.Zone / Time.Posix occurs on the anniversary
getNext : Time.Zone -> Time.Posix -> DayMonth a -> DayMonthYear
Returns a DayMonthYear record for anniversary's next occurrence
getLast : Time.Zone -> Time.Posix -> DayMonth a -> DayMonthYear
Returns a DayMonthYear record for anniversary's last occurrence