count-index.go
func (index *CountIndex) KNearest(point Point, k int, maxDistance Meters, accept func(p Point) bool) []Point {
	panic("Unsupported operation")
}
func (index *CountIndex) KNearest(point Point, k int, maxDistance Meters, accept func(p Point) bool) []Point {
	panic("Unsupported operation")
}
// KNearest just to satisfy an interface. Doesn't make much sense for count index.