add sugar methods/properties to AsyncResult
add sugar methods/properties to AsyncResult

* ar.wall_time = received - submitted
* ar.serial_time = sum of serial computation time
* ar.elapsed = time since submission (wall_time if done)
* ar.progress = (int) number of sub-tasks that have completed
* ar.wait_interactive(): prints progress
* len(ar) = # of tasks

ipython/ipython,ipython/ipython