code: func Pad(trytes Trytes, size int) Trytes {
  	if len(trytes) >= size {
  		return trytes
  	}
  	out := make([]byte, size)
  	copy(out, []byte(trytes))
  
  	for i := len(trytes); i < size; i++ {
  		out[i] = '9'
  	}
  	return Trytes(out)
  }
docs: // Pad pads the given trytes with 9s up to the given size.