Parser configuration :|
set_sswitch Set a new short option switch.
set_lswitch Set a new long option switch.
set_unknown Code to execute when a unknown option is read.
The faulty string is passed in parameter.
set_bad_position Code to execute when a bad position for a short argument is read.
The short argument and the string containing it are passed as parameters
with the description.
set_bad_number Code to execute when not enough argument are supplied.
The received number, expected number and description of the option are passed.
on_option long do Add an option to parse and code to execute when encoutered.
on_arg long with do is Add an argument to parse, with arguments number,
code to execute when encoutered and description printed on failure.