code: public static <T> Ix<T> merge(Iterable<? extends Iterable<? extends T>> sources) {
          return concat(sources);
      }
docs: Concatenates the elements of Iterable sources, provided as an Iterable itself, sequentially.
  <p>
  The result's iterator() forwards the remove() calls to the current iterator.
  <p>
  Note that merge and concat operations are the same in the Iterable world.
  @param <T> the common base type
  @param sources the Iterable sequence of source Iterables
  @return the new Ix instance
  @throws NullPointerException if sources is null
  @since 1.0
  @see #concat(Iterable)