Support short_name COLON value

[marwal-88]

I think Slop should support '-v:8' as well as '-v=8' and '-v 8'

suggesting this change in parser.rb

        # support `foo=bar`
        orig_flag = flag.dup
        # if match = flag.match(/([^=]+)=(.*)/) # OLD
        if match = flag.match(/([^=:]+)[=:](.*)/) # NEW
          flag, arg = match.captures
        end

Will make --president:Trump work as-well

[leejarvis]

Thanks for the suggestion. Are there other option parsers that support a colon? I've not seen it before. Open to it but I think some evidence of its usefulness would be good to add to the request.

[marwal-88]

I don't think it's wide-spread.. but I seen it from time to time. Nimgrep (by Andreas Rumpf - creator of the programming language Nim) supports it.. even seems to prefer it (according to documentation).