code: public StreamEx<T> prepend(T value) {
          return new StreamEx<>(new PrependSpliterator<>(spliterator(), value), context);
      }
docs: Returns a new {@code StreamEx} which is a concatenation of supplied value
  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>.
  
  @param value the value to prepend to the stream
  @return the new stream
  @since 0.5.4