[Request] Allow short option to not be first letter of long

[kescobo]

Is there a reason (other than preference) for this to error?

It seems pretty common to have single letter options that are different from the first letter of the long option, either for style (eg -x == --extract) or because multiple options start with the same letter (I ran into this because I have --debug and --default options, this means that only one can have a one-letter version).