How to quit macOS on last window closed

Issue #403

https://developer.apple.com/documentation/appkit/nsapplicationdelegate/1428381-applicationshouldterminateafterl?language=objc

The application sends this message to your delegate when the application’s last window is closed. It sends this message regardless of whether there are still panels open. (A panel in this case is defined as being an instance of NSPanel or one of its subclasses.)

If your implementation returns NO, control returns to the main event loop and the application is not terminated. If you return YES, your delegate’s applicationShouldTerminate: method is subsequently invoked to confirm that the application should be terminated.

func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
    return true
}