Restore properties on a function

Currently it's just stringifying the function - I should really be using `Function.prototype.toString` and restoring the function properties though (since a function is just another object).

Edit: Also for `RegExp`.

首先追蹤 issue 中描述的目前函式和 RegExp 字串化行為。將函式輸出與 Function.prototype.toString 進行比較，並判斷應如何還原屬性；當函式和 RegExp 值都保留所要求的表示形式和屬性時，即表示完成。

由索引模型根據 Issue 內容生成。