Add an option to change the current working directory

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Add -help option (short: -h)

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Fix "unknown option" behaviour

Also eliminate the one use of printf in the script.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>