
Examples:

     repeat every 10 sec after pause in 20 sec

     repeat every 30 sec

     11:17

     11:21:30

     from 11:00 to 17:00 every 30 minutes

     (11:17 + 21:19) * (monday + wednesday)

     from 11:00 to 17:00 every 30 minutes * (sunday + saturday)

Atomic schedulers:

   1) Exact time of day

            HH:mm[:ss]

      HH - hours  : 00 .. 23
      mm - minutes: 00 .. 59
      ss - seconds: 00 .. 59
      [] - content in [] is not mandatory

   2) Periodic run task every fixed duration (N1) after pause, if specified, in fixed duration (N2)

            repeat every N1 sec|min|hour [after pause in N2 sec|min|hour]

      N1, N2 - positive integer numbers
      [] - content in [] is not mandatory

   3) Period of time with fixed run every fixed time

      from HH:mm[:ss] to HH:mm[:ss] every N sec|min|hour

   4) Simple period of time in day. It can be used only with cooperation with another schedulers

      from HH:mm[:ss] to HH:mm[:ss]

   5) Day of week

      sunday|monday|tuesday|wednesday|thursday|friday|saturday

Scheduler combinations

   Some schedulers can be combined with two operator: plus `+` and multiply `*`. Multiply is more harder then plus.
   To exactly determine order of operation you can use square brackets, for example:

      from 8:00 to 18:00 every 1 hour * (mon + tue + wed + thu + fri)
