code: public static final <T> Transformer<T, T> orderedMergeWith(final Observable<T> other,
              final Comparator<? super T> comparator) {
          @SuppressWarnings("unchecked")
          Collection<Observable<T>> collection = Arrays.asList(other);
          return orderedMergeWith(collection, comparator);
      }
docs: <p>
  Returns the source {@link Observable} merged with the <code>other</code>
  observable using the given {@link Comparator} for order. A precondition
  is that the source and other are already ordered. This transformer
  supports backpressure and its inputs must also support backpressure.
  
  <p>
  <img src=
  "https://github.com/davidmoten/rxjava-extras/blob/master/src/docs/orderedMerge.png?raw=true"
  alt="marble diagram">
  
  @param other
  the other already ordered observable
  @param comparator
  the ordering to use
  @param <T>
  the generic type of the objects being compared
  @return merged and ordered observable