clustering-index.go
func (index *ClusteringIndex) KNearest(point Point, k int, maxDistance Meters, accept func(p Point) bool) []Point {
	return index.streetLevel.KNearest(point, k, maxDistance, accept)
}
func (index *ClusteringIndex) KNearest(point Point, k int, maxDistance Meters, accept func(p Point) bool) []Point {
	return index.streetLevel.KNearest(point, k, maxDistance, accept)
}
// KNearest returns the K-Nearest points near point within maxDistance, that match the accept function.