Compatible with iOS 9
Slide down to kill all app.
Long Press to make the app an "premium app" which can prevent it from being killed by the "killall" action -- it will be marked at the bottom with a red line.
IMPORTANT: Force touch settings changed in Preference, From "Enable" to "Disable" as force touch to kill all is stable now.
Now, long press home screen kills all the apps regardless of Premium Apps or Now Playing App.
Check them in settings.
More features will follow and check the preference for a more detailed instruction.