glg.go
func (g *Glg) CustomLogFunc(level string, f func() string) error {
	lv := g.TagStringToLevel(level)
	if g.isModeEnable(lv) {
		return g.out(lv, "%s", f())
	}
	return nil
}
func (g *Glg) CustomLogFunc(level string, f func() string) error {
	lv := g.TagStringToLevel(level)
	if g.isModeEnable(lv) {
		return g.out(lv, "%s", f())
	}
	return nil
}
// CustomLogFunc outputs custom level log returned from the function