code: public StreamEx<T> prepend(Collection<? extends T> collection) {
          return prependSpliterator(null, collection.spliterator());
      }
docs: Returns a new {@code StreamEx} which is a concatenation of the stream
  created from supplied collection and this stream.
  
  <p>
  This is a <a href="package-summary.html#StreamOps">quasi-intermediate
  operation</a> with <a href="package-summary.html#TSO">tail-stream
  optimization</a>.
  
  <p>
  May return this if the supplied collection is empty and non-concurrent.
  
  @param collection the collection to prepend to the stream
  @return the new stream
  @since 0.2.1