How can we declare consuming variadic arguments including `-` prefixed one in `OptionsType`

[norio-nomura]

jpsim/SourceKitten#174
Maybe that issue introduced since updating Commandant to the version that supports generating Unrecognized arguments error.

For fixing that, I tried:

    static func evaluate(m: CommandMode) -> Result<DocOptions, CommandantError<SourceKittenError>> {
        return create
            <*> m <| Option(key: "single-file", defaultValue: false, usage: "only document one file")
            <*> m <| Option(key: "module-name", defaultValue: "",    usage: "name of module to document (can't be used with `--single-file` or `--objc`)")
            <*> m <| Option(key: "objc",        defaultValue: false, usage: "document Objective-C headers")
            <*> m <| Argument(defaultValue: [], usage: "An argument list that consumes the rest of positional arguments")
    }

and got:

% cd Source/SourceKittenFrameworkTests/Fixtures
% sourcekitten doc --single-file Subscript.swift -j4 Subscript.swift
Unrecognized arguments: -j4

-j4 Subscript.swift are expected to use as arguments on launching child process.

[norio-nomura]

The child process is xcodebuild and may take another - prefixed arguments.

[mdiep]

We should probably support -- to explicitly end named arguments.

[norio-nomura]

Oh, -- works!
Thank you! 🙏