code: func NewUnsignedPermanode() *Builder {
  	bb := base(1, "permanode")
  	chars := make([]byte, 20)
  	_, err := io.ReadFull(rand.Reader, chars)
  	if err != nil {
  		panic("error reading random bytes: " + err.Error())
  	}
  	bb.m["random"] = base64.StdEncoding.EncodeToString(chars)
  	return bb
  }
docs: // NewUnsignedPermanode returns a new random permanode, not yet signed.