[execution interruption] add event_watch_signal() which allows registering for direct async interrupts outside the event loop
[execution interruption] initial support for execution interruption - allow calling js_eval_stop_execution from a different context and stop running loops
[execution interruption] add API for signaling on a serial device (e.g. sending CTRL-C)
[execution interruption] provide 'signal' handler for cli clients
[execution interruption] REPL: stop execution upon receiving signal
[execution interruption] don't perror() on signals
[execution interruption] signal handling such that SIGINT signals execution interruption