Feature Request: Change the permission of a note

There is no easy way to change note's permission in mass. While I can mass import Markdown note with this CLI, I cannot seem to control the permission of those notes with CLI. And it is a painstakingly long process to do it one-by-one on the web GUI.

It would be great if there is a command like this:
```
hackmd-cli chmod [NOTEID] [[-r|--readable] [owner|login|everyone]] [[-w|--writable] [owner|login|everyone]]
```

Example,
```
$ hackmd-cli chmod some-note-id -r everyone -w login
Permission of your note https://hackmd.io/some-note-id has changed.
Readable: everyone
Writable: login
```

首先檢查現有的 CLI 路徑，了解其如何大量匯入 Markdown 筆記以及如何處理筆記識別碼。接著確認提議的 chmod 引數如何對應至 HackMD 權限，並驗證命令的成功輸出，以及擁有者、登入使用者和所有人的可讀/可寫設定。

由索引模型根據 Issue 內容生成。