code: func (t *Tree) Last() (k []byte, v []byte) {
  	if q := t.last; q != nil {
  		q := &q.d[q.c-1]
  		k, v = q.k, q.v
  	}
  	return
  }
docs: // Last returns the last item of the tree in the key collating order, or
  // (zero-value, zero-value) if the tree is empty.