code: public static <E> Iterator<E> roundrobin(Iterator<E>... iterators) {
          return new RoundrobinIterator<E>(ArrayIterator.of(iterators));
      }
docs: Multiplexes an iterator of iterators into an iterator. Iteration stops
  when every element from every source has been consumed.
  <code>
  roundRobin([1,2], [3]) -> [1,3,2]
  </code>
  
  @param <E> the element type
  @param iterators the source iterators
  @return an iterator yielding multiplexed elements