this implements parsing and calculating calendarevents that have a
basic date component (year-mon-day) with the usual syntax options
(*, ranges, lists)
and some special events:
monthly
yearly/annually (like systemd)
quarterly
semiannually,semi-annually (like systemd)
includes some regression tests
the ~ syntax for days (the last x days of the month) is not yet
implemented
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
While we do not yet support the date specs for CalendarEvent the left
out "weekly" special expression[0] dies not requires that support.
It is specified to be equivalent with `Mon *-*-* 00:00:00` [0] and
this can be implemented with the weekday and time support we already
have.
[0]: https://www.freedesktop.org/software/systemd/man/systemd.time.html#Calendar%20Events
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
