HTTP::Date - date conversion routines

Changes for 6.06 - 2023-07-06T22:29:55Z

• Use copyright year rather than range (GH#18) (Olaf Alders)
• Replace "Test" with "Test::More" (GH#20) (James Raspass)
• Remove the executable bit from the test (GH#21) (James Raspass)
• Add support for Windows four-digit year format (GH#23) (Grant Street Group)