gstring.go
func Errorm(format string, args map[string]interface{}) error {
	f, a := gformat(format, args)
	return fmt.Errorf(f, a...)
}
func Errorm(format string, args map[string]interface{}) error {
	f, a := gformat(format, args)
	return fmt.Errorf(f, a...)
}
// interface similar to "fmt" package
// Errorm returns error instance with formatted error message.
// This is same as fmt.Errorf, but uses gstring formatting.