code: func NewBuffer(it SeriesIterator, delta int64) *BufferedSeriesIterator {
  	return &BufferedSeriesIterator{
  		it:       it,
  		buf:      newSampleRing(delta, 16),
  		lastTime: math.MinInt64,
  	}
  }
docs: // NewBuffer returns a new iterator that buffers the values within the time range
  // of the current element and the duration of delta before.