Multiple long arguments

Oftentimes it is useful to offer multiple long arguments for an option. A common case is a lengthy long argument for which you want to have a shorter version but the 1-char is not possible (e.g. because it's already assigned to other option).

For example, I have an option `DisableResourceWrites` with a long arg `--disableResourceWrites`, for which I would like it to shorten to `--drw` (`-d`, `-r` and `-w` are already taken).

I would like to use it like:
```cs
[Option(new [] { "disableResourceWrite", "drw" }, Required = false, HelpText = "Download resources even if they are already downloaded.")]
```

The help would show up like:

```
--disableResourceWrite, --drw Download resources even if they are already downloaded.
```

The unparsing would just choose the first long arg when short names are not preferred.