Invoking sambal via entrypoint script produces traceback on ctrl+c

You get the following traceback if you run the `sambal` script:

```
Traceback (most recent call last):
  File "/venv/sambal/bin/sambal", line 8, in <module>
    sys.exit(__main__())
TypeError: 'module' object is not callable
```

which you don't get if sambal is started via `python -m sambal`.