docs: add (+6.3.0) mark for an adopted feature in v6.3.0

[yoshinorin]

The current hexo.io does not support versioning. So, I marked (+6.3.0) to new features for v6.3.0. Because user can't understand which features are adopted in 6.3.0. Also I have already marked (+6.1.0) when release v6.1.0 same with this PR.

• refs: feat(helper/tagcloud): show_count option (hexojs/hexo#5047, hexojs/hexo#5048) #1902
• refs: feat(helper/toc): more flexible class name (hexojs/hexo#5010) #1886
• refs: feat(helper/is): add is_home_first_page() helper (hexojs/hexo#5006) #1885
• refs: feat(paginator): custom class name (hexojs/hexo#5001) #1873

Check List

• Others (Update, fix, translation, etc...)
  • Languages:
  • en English
  • ko Korean
  • pt-br Brazilian Portuguese
  • ru Russian
  • th Thai
  • zh-cn simplified Chinese
  • zh-tw traditional Chinese

[github-actions]

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