Date Class: Perform calculations with dates and times

This package consists of two classes meant for performing calculations with dates and times.

There is one class for manipulating dates and another for manipulate data spans.

The classes allow to add or subtract periods from dates and calculate the difference between two dates for various periods. Periods include Years, Quarters, Months, Weeks, Weekdays, Hours, Minutes, Seconds.

The classes return expected metrics plus begin and end of week, begin and end of quarter, begin and end of year, begin and end of month.