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.

首先追蹤選項宣告的表示方式、在說明中呈現的方式，以及在 unparsing 期間的處理方式。新增對多個長名稱的支援，使兩個名稱都出現在說明中；當不優先使用短名稱時使用第一個名稱，並確保現有的單一名稱選項繼續正常運作。

由索引模型根據 Issue 內容生成。