Add support for signal handling

[hex007]

Request to support signal handling. This would allow the application (launched during boot) to be cleanly closed if needed.

Currently applications exits and error message is printed
DATECODE sigHandler: Unhandled signal 2, terminating

[bitbank2]

Reasonable request - I'll add it and close this issue when it's ready.

[bitbank2]

Added and appears to work as it should. I added a ctrl-c handler; you can do a pull request to add others if you think they need to be added.

[hex007]

Thanks for this