code: function keyOfMin (o, func) {
                      if(!o || typeof o !== 'object') return o;
                      if(libs.object.size(o) === 0) return;
  
                      if(!(func instanceof Function)) func = undefined;
  
                      if(typeof o !== 'object') return o;
                      var min, minValue, minKey;
  
                      if(!func) {
                          min    = libs.object.first(o);
                          minKey = libs.object.keys(o)[0];
                          libs.object.each(o, 1, function (item, key) {
                              if(item <= min) {
                                  min    = item;
                                  minKey = key;
                              }
                          });
                      }
                      else {
                          min      = libs.object.first(o);
                          minValue = func.call(min, min);
                          minKey   = libs.object.keys(o)[0];
  
                          libs.object.each(o, 1, function (item, key) {
                              var value = func.call(item, item);
                              if(value <= minValue) {
                                  min      = item;
                                  minValue = value;
                                  minKey   = key;
                              }
                          });
                      }
                      return minKey;
                  }
docs: Returns the key of the item with the lowest 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 minimum item in the object collection.