code: function flatten(arr) {
              var result = [],
                  length = arr.length,
                  i;
              for (i = 0; i < length; i++) {
                  if (arr[i] instanceof Array) {
                      result = result.concat(utils.flatten(arr[i]));
                  } else {
                      result.push(arr[i]);
                  }
              }
              return result;
          }
docs: @method flatten()
  @for kity.Utils
  @grammar flatten(arr) => {Array}
  @description 返回给定数组的扁平化版本
  @param  {Array} arr 要扁平化的数组
  
  @example
  
  ```js
  var flattened = kity.Utils.flatten([[1, 2], [2, 3], [[4, 5], [6, 7]]]);
  console.log(flattened); // [1, 2, 3, 4, 5, 6, 7];
  ```