glg.go
func (g *Glg) SuccessFunc(f func() string) error {
	if g.isModeEnable(OK) {
		return g.out(OK, "%s", f())
	}
	return nil
}
func (g *Glg) SuccessFunc(f func() string) error {
	if g.isModeEnable(OK) {
		return g.out(OK, "%s", f())
	}
	return nil
}
// SuccessFunc outputs Success level log returned from the function