code: func NewSegmenter(r io.Reader) *Segmenter {
  	return &Segmenter{
  		r:            r,
  		segment:      SegmentWords,
  		maxTokenSize: MaxScanTokenSize,
  		buf:          make([]byte, 4096), // Plausible starting size; needn't be large.
  	}
  }
docs: // NewSegmenter returns a new Segmenter to read from r.
  // Defaults to segment using SegmentWords