code: function neighbourhoodSorter (a, b) {
    a = a.join(',');
    b = b.join(',');
    return a > b ? 1 : a < b ? -1 : 0;
  }
docs: Sort the neighbourhood from left to right, top to bottom, ...
  @param {Array} a First neighbour
  @param {Array} b Second neighbour
  @returns {number}