fix a crash if app/menuBar is nil (trying to release a nil object)
New actions and functionality for windows. Fixes quicksilver/quicksilver#1078

* Add a 'Show Application' for window objects
* Allow you to get menu items of windows and not just the app. This makes perfect sense, since in reality each window may have different menu items (enabled/disabled), depending on its state
* DRY
Make window actions work with the comma trick. Fixes quicksilver/quicksilver#832

DRY
Create a documenation file
Update documentation with new actions/info
Add info about menu items' details
Don't show empty windows for the 'show windows' action