Convert Stop() function to use variable length arguments

[KJ7LNW]

It may provide users additional information if the Stop() function can provide variable length arguments. We could then fold the more informative console errors (pr_err and pr_warn) into the output of the graphical error messages. See #47 for detail on one such example.

ref: https://www.tutorialspoint.com/c_standard_library/c_function_vsprintf.htm