Use stty interrupt setting instead of hardcoding Ctrl+C

I have the following stty config:

```
speed 38400 baud; line = 0;
intr = ^Q; susp = ^W;
-brkint -imaxbel
```

The key issue here is that interrupt is set to Ctrl+Q. Raw terminal apps will (hopefully) pick up on this and interrupt on Ctrl+Q instead of Ctrl+C. `promkit` does not do this however. Instead, it ONLY responds to Ctrl+C.