refactor: utilize hexo-util

[SukkaW]

What does it do?

Utilize hexo-util's CacheStream() & Cache();

How to test

git clone -b utilize-hexo-util-cache https://github.com/sukkaw/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage decreased (-0.01%) to 97.092% when pulling aed8240 on SukkaW:utilize-hexo-util-cache into a381dda on hexojs:master.

[curbengh]

Slightly off-topic to this PR, would caching helps external_link filter? If assuming it's possible to cache all <a> in all pages (including posts), since there bounds to be repetitive links (especially navigation links), maybe it can help (even just a tiny bit, if memory usage doesn't increase).

[SukkaW]

@curbengh Cache is already been enabled in hexo-util's isExternalLink() and I think it is enough.

[curbengh]

what about caching every <a></a>, so it returns processed <a></a>. I'm assuming object cache is faster than String.replace().

[SukkaW]

@curbengh I will give it a try in a separate PR.

[curbengh]

tested