Add option to import custom extractor binary

[RyanBram]

Hi, Developers. Thanks for reviving the great Universal Extractor. I have a suggestion.

Can you add an option to import custom extractor binary which isn't in the current list by providing user an option to browse the extractorbinary, assign a command line argument for it, and asociating extension for it. It will be very useful if the archive is something rare and can only be opened by custom extractor. Sorry for my english.

Thanks.

[GitHubRulesOK]

technically plugins adresses this request, however see my comment in #31 (& enhances #30) Here the suggestion would be to allow user to specify more than one "special" extractor and allow for seperate commands lines regardless if cmd or exe is the same or different