docs: function asyncFilter(promise, iterator, scope, limit) {
      return asyncArray(asyncLoop(promise, iterator, scope, limit).chain(function (results) {
          var loopResults = results.loopResults, resultArr = results.arr;
          return (isArray(resultArr) ? resultArr : [resultArr]).filter(function (res, i) {
              return loopResults[i];
          });
      }));
  }