read.go
func (c *ConfigFile) AppendFiles(files ...string) error {
	if len(c.fileNames) == 1 && c.fileNames[0] == "" {
		return fmt.Errorf("Cannot append file data to in-memory data")
	}
	c.fileNames = append(c.fileNames, files...)
	return c.Reload()
}
func (c *ConfigFile) AppendFiles(files ...string) error {
	if len(c.fileNames) == 1 && c.fileNames[0] == "" {
		return fmt.Errorf("Cannot append file data to in-memory data")
	}
	c.fileNames = append(c.fileNames, files...)
	return c.Reload()
}
// AppendFiles appends more files to ConfigFile and reload automatically.