iv_fatal aborts the running program, after possibly emitting an error
fmt parameter is a
format string, the message to be logged.
If no handler is set (the default), the formatted message will be sent
syslog, with critical severity. Otherwise the
handler as set by
iv_set_fatal_msg_handler will be used instead.
iv_fatal is also used internally by ivykis, whenever a fatal situation is
iv_set_fatal_msg_handler can be used to set an alternative (as opposed to
syslog) function to call from
iv_fatal, and its argument should be a function that does not return, and takes
a single string as argument - the formatted error message.