switched to using atexit instead of handling signals

[johan-bjareholt]

With this the modules do not even exit properly with SIGINT (ctrl+c) and doesn't handle when it crashes any better.

[ErikBjare]

Oh, that sucks. I thought atexit was a neat way to manage cases like this.

Edit: Someone on SO apparently knew this

Do you think try: ...; finally: ... would work?

Alternatively we could just make all signals call sys.exit() which would trigger the atexit.

[ErikBjare]

Won't merge, closing.