ParseResultType is rarely handled properly

[vogel]

Out of 4 values of ParseResultType, one is not used at all ShortCircuitSame and ShortCircuitAll is only possible for Options.

I tried to add and Arg with ShortCircuitAll to be able to implement subcommands, but it simply didn't work (as Arg::parse only returns Matched or failed values, no matter what valueRef->setValue returns).