durafmt.go
func ParseStringShort(input string) (*Durafmt, error) {
	if input == "0" || input == "-0" {
		return nil, errors.New("durafmt: missing unit in duration " + input)
	}
	duration, err := time.ParseDuration(input)
	if err != nil {
		return nil, err
	}
	return &Durafmt{duration, input, true}, nil
}
func ParseStringShort(input string) (*Durafmt, error) {
	if input == "0" || input == "-0" {
		return nil, errors.New("durafmt: missing unit in duration " + input)
	}
	duration, err := time.ParseDuration(input)
	if err != nil {
		return nil, err
	}
	return &Durafmt{duration, input, true}, nil
}
// ParseStringShort creates a new *Durafmt struct from a string, short form
// returns an error if input is invalid.