Fix sublanguages highlight

[l-vo]

Highlightjs has a sublanguages feature which allows some languages to incorporate and highlight another language inside it. When I use a sublanguage in Hexo, it doesn't work:

This PR make the sublanguages functional:

The sublanguage feature requires that the sublangage definition is loaded. But Hexo only load the definition of the main language of the code chunk. I suggest to always load all language definitions, like it's done in highlightjs library and in hexo-util tests (so the tests are currently not totally right since the definitions loaded in tests are not the same as the definitions actually loaded by hexo-utils).

Also, it could be possible to dynamically load sublanguages but it will make hexo-util too closely coupled with hightlighjs IMHO.

[coveralls]

Coverage increased (+0.7%) to 95.897% when pulling 5e0deb9 on l-vo:fix_sublanguages_highlight into 95f791a on hexojs:master.

[segayuu]

This PR is loosely coupled or a trade-off with memory, and it is difficult to decide which one to prioritize.
Whether this behavior should be changed as hexo-util libraries remains in doubt.
However, I acknowledge that it is not good to use sub language features at Hexo in the current situation.