Usage

    //New a cron with timezone. 
    c := cron.New(0) 
    c.AddFunc("0 30 * * * *", func() { fmt.Println("Every hour on the half hour") })
    c.AddFunc("@hourly",      func() { fmt.Println("Every hour") })
    c.AddFunc("@every 1h30m", func() { fmt.Println("Every hour thirty") })
    c.Start()
    ..
    // Funcs are invoked in their own goroutine, asynchronously.
    ...
    // Funcs may also be added to a running Cron
    c.AddFunc("@daily", func() { fmt.Println("Every day") })
    ..
    // Inspect the cron job entries' next and previous run times.
    inspect(c.Entries())
    ..
    c.Stop()  // Stop the scheduler (does not stop any jobs already running).