geohash.go
func DecodeCenter(hash string) (lat, lng float64) {
	box := BoundingBox(hash)
	return box.Center()
}
func DecodeCenter(hash string) (lat, lng float64) {
	box := BoundingBox(hash)
	return box.Center()
}
// DecodeCenter decodes the string geohash to the central point of the bounding box.