Multiple changes. Refer to the description.

1. Refactored Executor.
2. Added comments to Notifier, JNotifier, WatchKey, Watchers.
3. JNotifyWatchKey.
4. Added clear all functionality to Watchers.
5. Fixed issue - 10. Right now one folder can be monitored by two
watchers. Can this be avoided?
6. Updated the WatchKey. Now, instead of just the actual key, it also
looks for a folder path uniqueness.