kill background processes on exit

I run an application using bubblewrap that forks off a number of background processes. When closing the application, the background processes are not always cleaned up, so if I run `lsns`, I will still see `bwrap` running and the background processes as its children. To clean up the namespace, I have to send the `KILL` signal to `bwrap`.

Is it possible for `bwrap` to automatically kill everything in the namespace when the foreground process terminates? Or is there a reason why that wouldn't be appropriate?

BTW, bubblewrap is awesome; thanks for writing it!