code: func (rb *RegretableReader) Forget() {
  	if rb.overflow {
  		panic("forgetting after overflow makes no sense")
  	}
  	rb.r = 0
  	rb.w = 0
  }
docs: // Will "forget" everything read so far.
  //	rb := NewRegretableReader(bytes.NewBuffer([]byte{1,2,3}))
  //	var b = make([]byte,1)
  //	rb.Read(b) // b[0] = 1
  //	rb.Forget()
  //	rb.Read(b) // b[0] = 2
  //	rb.Regret()
  //	ioutil.ReadAll(rb.Read) // returns []byte{2,3},nil