code: func NewMultiIterator(reverse bool, iterators ...KVIterator) *MultiIterator {
  	// reuse backing array
  	lessComp := -1
  	if reverse {
  		lessComp = 1
  	}
  	mi := &MultiIterator{
  		iterators:     iterators,
  		iteratorOrder: make(map[KVIterator]int),
  		lessComp:      lessComp,
  	}
  	mi.init()
  	return mi
  }
docs: // MultiIterator iterates in order over a series o