fix(highlight): decouple 'wrap' and 'hljs'

[curbengh]

Currently, enabling hljs always disable wrap, but I noticed that it is actually not necessary. I tested hljs: true + wrap: true with darcula theme, code highlighting works fine.

Noticed while testing hexojs/hexo#3865

---

line_number: true # or gutter: true
hljs: true
wrap: false

Since enabling line_number will also enable wrap, this behavior doesn't change.

---

line_number: false
hljs: true
wrap: true

With this PR, it is possible to enable both hljs and wrap, so user can use hljs-* prefix in css classes while wrapping the codeblock in <table>. This can make upgrading the hljs syntax slightly easier.

[coveralls]

Coverage decreased (-0.008%) to 95.246% when pulling ef769c2 on curbengh:hljs-wrap into ad3541e on hexojs:master.