Clon provides two utility functions to inquire on the current status
of the command-line.
The function cmdline-options-p returns true if there are still
unprocessed options on the command-line. The function cmdline-p
returns true if there’s anything left on the command-line, that is,
either unprocessed options, or a remainder. A potential use of
cmdline-p at a very early stage of your application could be to
automatically display a help string if the command-line is effectively
empty.