whereWithinMiles method
Returns an object with key point values near the point given and within the maximum distance given.
Implementation
void whereWithinMiles(
    String column, ParseGeoPoint point, double maxDistance) {
  final double latitude = point.latitude;
  final double longitude = point.longitude;
  queries.add(MapEntry<String, dynamic>(_singleQuery,
      '"$column":{"\$nearSphere":{"__type":"GeoPoint","latitude":$latitude,"longitude":$longitude},"\$maxDistanceInMiles":$maxDistance}'));
}