code: @SafeVarargs
      public final StreamEx<T> prepend(T... values) {
          return prependSpliterator(null, Spliterators.spliterator(values, Spliterator.ORDERED));
      }
docs: Returns a new {@code StreamEx} which is a concatenation of supplied
  values 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 no values are supplied.
  
  @param values the values to prepend to the stream
  @return the new stream