Add progress method for promises

[fahad86]

Useful for use-cases like file-upload etc

Q library implementation:
`
/**

• Attaches a listener that can respond to progress notifications from a
• promise's originating deferred. This listener receives the exact arguments
• passed to deferred.notify.
• @param {Any*} promise for something
• @param {Function} callback to receive any progress notifications
• @returns the given promise, unchanged
  */
  Q.progress = progress;
  function progress(object, progressed) {
  return Q(object).then(void 0, void 0, progressed);
  }

Promise.prototype.progress = function (progressed) {
return this.then(void 0, void 0, progressed);
};

/**

• Turns an array of promises into a promise for an array. If any of
• the promises gets rejected, the whole array is rejected immediately.
• @param {Array*} an array (or promise for an array) of values (or
• promises for values)
• @returns a promise for an array of the corresponding values
  */
  // By Mark Miller
  // http://wiki.ecmascript.org/doku.php?id=strawman:concurrency&rev=1308776521#allfulfilled
  Q.all = all;
  function all(promises) {
  return when(promises, function (promises) {
  var pendingCount = 0;
  var deferred = defer();
  array_reduce(promises, function (undefined, promise, index) {
  var snapshot;
  if (
  isPromise(promise) &&
  (snapshot = promise.inspect()).state === "fulfilled"
  ) {
  promises[index] = snapshot.value;
  } else {
  ++pendingCount;
  when(
  promise,
  function (value) {
  promises[index] = value;
  if (--pendingCount === 0) {
  deferred.resolve(promises);
  }
  },
  deferred.reject,
  function (progress) {
  deferred.notify({ index: index, value: progress });
  }
  );
  }
  }, void 0);
  if (pendingCount === 0) {
  deferred.resolve(promises);
  }
  return deferred.promise;
  });
  }
  `

[suguru03]

@fahad86 Thanks for the feature idea!
Looks useful! I will investigate it. 😄