Minimal five-field cron expressions: minute hour day-of-month month day-of-week.
Supports *, numbers, ranges (a-b), steps (*/n, a-b/n), lists
(a,b,c), and the nicknames @hourly, @daily, @midnight, @weekly,
@monthly. Day-of-week is 0-6 with 0 = Sunday (7 also accepted as Sunday).
Summary
Functions
Does the minute containing datetime (UTC) match?
Parse an expression. Returns {:ok, t} or {:error, reason}.
Truncate a datetime to its minute slot.