func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
	r.prevRune = -1
	if r.i >= int64(len(r.s)) {
		return 0, nil
	}
	b := r.s[r.i:]
	m, err := w.Write(b)
	if m > len(b) {
		panic("bytes.Reader.WriteTo: invalid Write count")
	}
	r.i += int64(m)
	n = int64(m)
	if m != len(b) && err == nil {
		err = io.ErrShortWrite
	}
	return
}