stack.go
func (fb *fileBlock) writeTo(writer io.WriteSeeker, offset int64) error {
	_, err := writer.Seek(offset, os.SEEK_SET)
	if err != nil {
		return err
	}
	return binary.Write(writer, binary.LittleEndian, *fb)
}
func (fb *fileBlock) writeTo(writer io.WriteSeeker, offset int64) error {
	_, err := writer.Seek(offset, os.SEEK_SET)
	if err != nil {
		return err
	}
	return binary.Write(writer, binary.LittleEndian, *fb)
}
// Write meta-info to specified place