Individual views may now be used by themselves!

If you want, you can now just use the yearly or monthly view in your app. The models for these views have been made public and refined for greater flexibility. To use these views by themselves, use the correct ObservableObject: MonthlyCalendarManager or YearlyCalendarManager.

Major change: The naming of a delegate function has also been changed: func calendar(didSelectDate date: Date) -> func calendar(didSelectDay date: Date).