refactor(comment): split comment provider/allow custom

[cubesky]

What kind of change does this PR introduce? (check one with "x")

• Bug fix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

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Description

Split Comment provider to single folder to avoid conflict with update.
Now everyone can custom their own comment provider easily.

How to Custom comment provider ?

1. Create new folder in layout\_widget\comment\ .
2. Create three new file with common.ejs enter.ejs main.ejs.
3. Put codes in these file.
   • Insert common js file in common.ejs.
   • Setup div and main.ejs in enter.ejs.
   • Init comment provider in main.ejs
4. Change your comment.use in _config.yml to the name of your custom folder.
5. Enjoy!

You can also see disqus folder to learn more.

Tips:
You can create a comment.yml in your site root_folder/source/_data/ and use site.data.comment.xxxx to use them. Eg. comment.yml

comment_js: https://example.com/example.js

And use <%- site.data.comment.comment_js %> in your custom ejs files to use this.

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Verification steps

Make your own custom comment provider following How to Custom comment provider ? and run hexo s