code: public StreamEx<T> append(T value) {
          return appendSpliterator(null, new ConstSpliterator.OfRef<>(value, 1, true));
      }
docs: Returns a new {@code StreamEx} which is a concatenation of this stream
  and the supplied value.
  
  <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 append to the stream
  @return the new stream
  @since 0.5.4