Re-enable KeyboardInterrupt on Ctrl+C?

[devvmh]

Hi, when I import soundmeter into my flask app, I believe it's breaking the default Ctrl+C behaviour because the sigint_handler doesn't raise KeyboardInterrupt. I believe if you simply adding raise KeyboardInterrupt to the end of sigint_handler, this would work correctly again. However, not sure if this was intentional or if it'll mess up daemonized mode.

Am I correct? Is this something worth fixing? If so, I can make the PR if it helps