The functionality of required() in Opt

[bigwater]

I checked the ``required()" function of an Opt and try to use it to represent a mandatory option in my project, however, seems it only affects the printed information of --help.

Is the "required()" or "isOptional()" function going to raise an exception when the option is not present when parsing the command line?

Checked the code, seems it is not implemented.
// !TBD Check missing required options

Thank you.

[rpavlik]

Duplicate of #39