code: public IntStreamEx pairMap(IntBinaryOperator mapper) {
          return delegate(new PairSpliterator.PSOfInt(mapper, null, spliterator(), PairSpliterator.MODE_PAIRS));
      }
docs: Returns a stream consisting of the results of applying the given function
  to the every adjacent pair of elements of this stream.
  
  <p>
  This is a <a href="package-summary.html#StreamOps">quasi-intermediate
  operation</a>.
  
  <p>
  The output stream will contain one element less than this stream. If this
  stream contains zero or one element the output stream will be empty.
  
  @param mapper a non-interfering, stateless function to apply to each
  adjacent pair of this stream elements.
  @return the new stream
  @since 0.2.1