code: function keyOfMax (o, func) {
                      if(!o || typeof o !== 'object') return o;
                      if(libs.object.size(o) === 0) return;
  
                      if(!(func instanceof Function)) func = undefined;
                      var max, maxValue, maxKey;
  
                      if(!func) {
                          max    = libs.object.first(o);
                          maxKey = libs.object.keys(o)[0];
                          libs.object.each(o, 1, function (item, key) {
                              if(item >= max) {
                                  max    = item;
                                  maxKey = key;
                              }
                          });
                      }
                      else {
                          max      = libs.object.first(o);
                          maxKey   = libs.object.keys(o)[0];
                          maxValue = func.call(max, max);
  
                          libs.object.each(o, 1, function (item, key) {
                              var value = func.call(item, item);
                              if(value >= maxValue) {
                                  if(value >= maxValue) {
                                      max      = item;
                                      maxValue = value;
                                      maxKey   = key;
                                  }
                              }
                          });
                      }
                      return maxKey;
                  }
docs: Returns the key of the item with the highest value in the object.
  @param {Object} o The object to operate on.
  @param {Function=} func If passed, the function will be invoked for each item in the object collection.
  @return {*} The maximum item in the object collection.