code: public EntryStream<K, V> prepend(K k1, V v1, K k2, V v2) {
          @SuppressWarnings("unchecked")
          SimpleImmutableEntry<K, V>[] array = new SimpleImmutableEntry[] { new SimpleImmutableEntry<>(k1, v1),
                  new SimpleImmutableEntry<>(k2, v2) };
          return prependSpliterator(null, Spliterators.spliterator(array, Spliterator.ORDERED));
      }
docs: Returns a new {@code EntryStream} which is a concatenation of two
  supplied key-value pairs 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 k1 the key of the first {@code Entry} to prepend to this stream
  @param v1 the value of the first {@code Entry} to prepend to this stream
  @param k2 the key of the second {@code Entry} to prepend to this stream
  @param v2 the value of the second {@code Entry} to prepend to this stream
  @return the new stream
  @since 0.2.3