code: function arrayFlatten(arr, level) {
          var self = this;
          var result = [];
          var current = 0;
          level = level || Infinity;
  
          self._forEach(arr, function (el) {
              if (validateHelpers.isArray(el) && current < level) {
                  result = result.concat(self.arrayFlatten(el, level, current + 1));
              } else {
                  result.push(el);
              }
          });
          return result;
      }
docs: Returns a flattened, one-dimensional copy of the array.
  You can optionally specify a limit, which will only flatten to that depth.
  
  @param  {Array}   arr              Array to flatten
  @param  {Integer} level[Infinity]  Depth
  @return {Array}