Major Description
I would like to propose to add a new method called "stop()" in Droid classes: Droid, AbstractDroid, and TaskMaster to terminate a running droid object and clear up any associated resources.
Background: I was integrating Droids with a search application which can take advantage of MultiThreadedTaskManager. Existing implementation of Droid (i.e. AbstractDroid and CrawlingDroid) does not allow easy access to stop the droid and clear the resources such as to clear the queue, clear the history and shutdown the pool used by multi-threaded task master even though the MultiThreadedTaskManager has a public method called "stop()" to shutdown the thread pool.
Justification: I realize when I add a front UI for user to configure the crawler, it's very common for users to add or edit starting URLs, then stop the crawler and restart the crawler with the new configuration. So it would be nice to expose the stop() functionality for the crawler, task master and droid.
