On AnyKey pressed:
>System: Exit Application
That's the basic gist of it.
Making a working pause button is trickier because you have to set up a time scale, and have your events correspond with said time scale, to pause it. I would recommend reading up a lot on the delta-time stuff to get a better grasp of what you want to do.
Because to pause a game, you need to set the time-scale of the game to 0 (time-scale at runtime is at 1.0). You just need to make sure that the rest of the game's objects and events are running on that time-scale, which is a process I am not 100% sure how to accomplish.
Of course, I might be speaking of outdated knowledge since I haven't picked up the latest version of C2 for a few months. I don't think any magical pause plugin has been created, though.