在 GitHub 上添加一个按钮，用于直接预览 HTML 和媒体文件。
Adds a button on GitHub to preview HTML and media files directly. Uses GitHub Preview.
This script works on private repositories as well, as long as you have access to the files. To do that, this script simply issues a HEAD request to the raw file URL, follows the redirect, and use the final URL which would include a token. However, HTML files referencing other files (e.g. CSS, JS) may not work properly due to the lack of token in their URLs.
