Fix return code for --help and --version

[rotty]

When the --help' or--version' command-line options were given, quicktun would exit with exit status 1, although the requested action was fulfilled without encountering an error. With this change, these options now will result in a zero exit status.

In addition, with both of these option, the header printed was partially overlapping with the message printed by the option, so the header is now printer after option processing.