The current (r59) argument parsing is not GNU/POSIX compliant ("-gui": contains a single hyphen, but more than one character).
Additionally the "optparse" python module (available since python v2.3) is used for generating a help message and general error handling.
This switch to the "optparse" module will ease the addition of more options (e.g. defining a x/y/z range for batch conversion) in the future.
Currently the "-gui" option can't be used in combination with the "outputfile" argument. This should be fixed later.