code: public AVQuery<T> whereWithinKilometers(String key, AVGeoPoint point, double maxDistance) {
      conditions.whereWithinKilometers(key, point, maxDistance);
      return this;
    }
docs: Add a proximity based constraint for finding objects with key point values near the point given
  and within the maximum distance given. Radius of earth used is 6371.0 kilometers.
  
  @param key The key that the AVGeoPoint is stored in.
  @param point The reference AVGeoPoint that is used.
  @param maxDistance Maximum distance (in kilometers) of results to return.
  @return