Release Name: 0.5.1

Notes:
* License changed to Artistic 2.0
* ChangeNotify#wait now more robust


Changes:
* License changed to Artistic 2.0.
* The ChangeNotify#wait method is now slightly more robust.
* Renamed test file to test_win32_changenotify.rb.
* Some gemspec updates, including license and description.
* Renamed example file to example_win32_changenotify.rb to avoid any
  confusion with actual test files.
* Removed the doc/changenotify.txt file because I felt it was redundant.
* Added an example rake task.