code: public EntryStream<K, V> append(K key, V value) {
          return appendSpliterator(null, new ConstSpliterator.OfRef<>(new SimpleImmutableEntry<>(key, value), 1, true));
      }
docs: Returns a new {@code EntryStream} which is a concatenation of this stream
  and the supplied key-value pair.
  
  <p>
  This is a <a href="package-summary.html#StreamOps">quasi-intermediate
  operation</a>.
  
  @param key the key of the new {@code Entry} to append to this stream
  @param value the value of the new {@code Entry} to append to this stream
  @return the new stream