STDIN/STDOUT reference `-` can't be used as argument

In most *nix tooling, `-` can be used as an alias for either `/dev/stdin` or `/dev/stdout` (depending on what is expected in the context). I can't figure out how to pars thet using this library. It looks like it is parsable as an argument after a `--` separator, but in all other circumstances (where it might be expected)


Sample expected usage:

```
$ my_cmd -f -
```