add new features, OneTimeJob and Job.RunNow() (#646)

errors.go

@@ -12,6 +12,7 @@ var (
 	ErrDurationRandomJobMinMax       = fmt.Errorf("gocron: DurationRandomJob: minimum duration must be less than maximum duration")
 	ErrEventListenerFuncNil          = fmt.Errorf("gocron: eventListenerFunc must not be nil")
 	ErrJobNotFound                   = fmt.Errorf("gocron: job not found")
+	ErrJobRunNowFailed               = fmt.Errorf("gocron: Job: RunNow: scheduler unreachable")
 	ErrMonthlyJobDays                = fmt.Errorf("gocron: MonthlyJob: daysOfTheMonth must be between 31 and -31 inclusive, and not 0")
 	ErrMonthlyJobAtTimeNil           = fmt.Errorf("gocron: MonthlyJob: atTime within atTimes must not be nil")
 	ErrMonthlyJobAtTimesNil          = fmt.Errorf("gocron: MonthlyJob: atTimes must not be nil")
@@ -22,6 +23,7 @@ var (
 	ErrNewJobTaskNotFunc             = fmt.Errorf("gocron: NewJob: Task.Function must be of kind reflect.Func")
 	ErrNewJobWrongNumberOfParameters = fmt.Errorf("gocron: NewJob: Number of provided parameters does not match expected")
 	ErrNewJobWrongTypeOfParameters   = fmt.Errorf("gocron: NewJob: Type of provided parameters does not match expected")
+	ErrOneTimeJobStartDateTimePast   = fmt.Errorf("gocron: OneTimeJob: start must not be in the past")
 	ErrStopExecutorTimedOut          = fmt.Errorf("gocron: timed out waiting for executor to stop")
 	ErrStopJobsTimedOut              = fmt.Errorf("gocron: timed out waiting for jobs to finish")
 	ErrStopSchedulerTimedOut         = fmt.Errorf("gocron: timed out waiting for scheduler to stop")