code: function asyncPowerSet(arr) {
      return asyncArray(when(arr).chain(function (result) {
          return powerSet.call(array, normalizeResult(result));
      }));
  }
docs: Async version of {@link comb.array.powerSet}.
  
  ```
  function asyncArr(){
  var ret = new comb.Promise();
  process.nextTick(ret.callback.bind(ret, [1,2,3,4,5]);
  return ret.promise;
  }
  
  comb.async.array(asyncArr()).powerSet().then(function(set){
  console.log(set); //[ [], [ 1 ], [ 2 ], [ 1, 2 ], [ 3 ], [ 1, 3 ], [ 2, 3 ], [ 1, 2, 3 ] ]
  });
  
  comb.async.powerSet(asyncArr()).then(function(set){
  console.log(set); //[ [], [ 1 ], [ 2 ], [ 1, 2 ], [ 3 ], [ 1, 3 ], [ 2, 3 ], [ 1, 2, 3 ] ]
  });
  
  ```
  
  @static
  @memberof comb.async
  @name powerSet