title: Send request to web service when app gets killed? (Swift 3)
body: <p>It's very important for my app to be notified every time the user kills my app (not moving it to the background, but actually quitting it altogether by double-tapping the Home button and swiping my app screenshot up). I know <code>applicationWillTerminate()</code> barely ever gets called, so I was wondering what the safest way is to be notified when a user will kill the app. It seems very unlikely that Apple hasn't provided ANY form of solution for this, as a lot of iOS users make it a custom to kill apps when they're done using it, so it would be really really REALLY weird if it would be impossible to catch this event. The only thing I need to do is fire off a <code>URLRequest</code> to send some updating instructions to my web service.</p>