code: function asyncDifference() {
      return asyncArray(when.apply(null, argsToArray(arguments)).chain(function (result) {
          return difference.apply(array, normalizeResult(result).map(function (arg) {
              return isArray(arg) ? arg : [arg];
          }));
      }));
  }
docs: Async version of {@link comb.array.difference}.
  
  ```
  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()).difference([3,4,5]).then(function(diff){
  console.log(diff); //[1,2]
  })
  
  comb.async.difference(asyncArr(), [3,4,5]).then(function(diff){
  console.log(diff); //[1,2]
  })
  
  ```
  
  @static
  @memberof comb.async
  @name difference