code: function store(hmap){
  
              var _ = {
                  // data is a two dimensional array
                  // a datapoint gets saved as data[point-x-value][point-y-value]
                  // the value at [point-x-value][point-y-value] is the occurrence of the datapoint
                  data: [],
                  // tight coupling of the heatmap object
                  heatmap: hmap
              };
              // the max occurrence - the heatmaps radial gradient alpha transition is based on it
              this.max = 1;
  
              this.get = function(key){
                  return _[key];
              };
              this.set = function(key, value){
                  _[key] = value;
              };
          }
docs: store object constructor a heatmap contains a store the store has to know about the heatmap in order to trigger heatmap updates when datapoints get added