[tz] USNO steps gingerly into the daylight saving mess

Last month the US Naval Observatory's Astronomical Applications Department published a web page that displays daylight saving starting and ending dates for US rules since 1967. A web page lets you enter a year like 1967 and the response will tell you start and end dates for that year. There is also an API that returns the data in a JSON format. Only US federal rules are supported, and only years from 1967 through 9999. See: https://aa.usno.navy.mil/data/docs/daylight_time.php