internal/dic/index.go
func (idx IndexTable) WriteTo(w io.Writer) (n int64, err error) {
	n, err = idx.Da.WriteTo(w)
	var b bytes.Buffer
	enc := gob.NewEncoder(&b)
	if err = enc.Encode(idx.Dup); err != nil {
		return
	}
	x, err := b.WriteTo(w)
	if err != nil {
		return
	}
	n += x
	return
}
func (idx IndexTable) WriteTo(w io.Writer) (n int64, err error) {
	n, err = idx.Da.WriteTo(w)
	var b bytes.Buffer
	enc := gob.NewEncoder(&b)
	if err = enc.Encode(idx.Dup); err != nil {
		return
	}
	x, err := b.WriteTo(w)
	if err != nil {
		return
	}
	n += x
	return
}
// WriteTo saves a index table.