Mo date utilities.

Changes for 0.04 - 2024-03-31T19:52:38+02:00

• Add error checks to check_date_order().
• Add possibility to use check_date_order() on DateTime objects.
• Add tests for check_date().
• Add tests for check_date_dmy().
• Add tests for check_date_order().
• Rewrite "," to "=>" in err().