Starts listening for the specified POSIX signal.
Note that if a default signal handler exists for the signal, it will be disabled by using this function.
|sig||The number of the signal to listen for|
|on_signal||Callback that gets called whenever a matching signal gets received|
Returns an identifier that identifies the resource associated with
the signal. Giving up ownership of this resource using
will re-enable the default signal handler, if any was present.
For any error condition,
SignalListenID will be returned