code: public static <T> Collection<T> flatten(Iterable<? extends Iterable<T>> iterable)
      {
          return Iterate.flatCollect(iterable, Functions.<Iterable<T>>identity());
      }
docs: Flattens a collection of collections into one "flat" collection.
  
  @param iterable A list of lists, e.g. { { 1, 2, 3 }, { 4, 5 }, { 6 } }
  @return A flattened list, e.g. { 1, 2, 3, 4, 5, 6 }