func NewBuffer(delta int64) *BufferedSeriesIterator {
	return NewBufferIterator(&NoopSeriesIt, delta)
}
NewBuffer returns a new iterator that buffers the values within the time range
of the current element and the duration of delta before, initialized with an
empty iterator. Use Reset() to set an actual iterator to be buffered.
package storage
import (
	"math"
)
type BufferedSeriesIterator struct {
	it    SeriesIterator
	buf   *sampleRing
	delta int64
	lastTime int64
	ok       bool
}