Do not require file to be present

[rejeep]

Evaling this:

(progn
  (require 'commander)
(defun foo ()
  (print "foo"))
(commander
 (command "foo" foo))
(commander-print-usage))

Will result in: f-filename: Wrong type argument: stringp, nil.

This is because the usage information is based on filename if the name directive is not used.