func Every(interval time.Duration, options ...EveryOption) Schedule {
	every := &every{}
	for _, option := range options {
		option(every)
	}
	first := true
	return func() (time.Duration, error) {
		var err error
		if first && every.skipFirst {
			err = ErrSkip
		}
		first = false
		return interval, err
	}
}
func Every(interval time.Duration, options ...EveryOption) Schedule {
	every := &every{}
	for _, option := range options {
		option(every)
	}
	first := true
	return func() (time.Duration, error) {
		var err error
		if first && every.skipFirst {
			err = ErrSkip
		}
		first = false
		return interval, err
	}
}
// Every returns a Schedule that always returns the given time interval.