/// <summary>
        /// Removes a BetterProximityChecker from collection.
        /// </summary>
        /// <param name="checker"></param>
        public static void RemoveChecker(FastProximityChecker checker)
        {
            int index = _instance._checkers.IndexOf(checker);

            if (index != -1)
            {
                if (index < _instance._nextIndex)
                {
                    _instance._nextIndex--;
                }

                _instance._checkers.RemoveAt(index);
            }
        }
 /// <summary>
 /// Adds a BetterProximityChecker to collection.
 /// </summary>
 /// <param name="checker"></param>
 public static void AddChecker(FastProximityChecker checker)
 {
     _instance._checkers.Add(checker);
 }