code: public static <T> Ix<T> orderedMerge(Iterable<? extends Iterable<? extends T>> sources, Comparator<? super T> comparator) {
          return new IxOrderedMergeIterable<T>(nullCheck(sources, "sources is null"), nullCheck(comparator, "comparator is null"));
      }
docs: Merges items from an Iterable sequence of Iterable sequences, picking
  the smallest item (according to a custom comparator) from all those inner
  Iterables until all sources complete.
  @param <T> the value type
  @param sources the Iterable sequence of Iterables
  @param comparator the comparator to compare items and pick the one that returns negative will be picked
  @return the new Ix instance
  @since 1.0