highlightjs parameters are ignored

Thanks for a theme with such an awesome navigation!

It seems highlightjs parameters (such as `hljs_style` and `hljs_languages`) are not respected in Windmill despite being fully supported in mkdocs. I.e. following code works fine with mkdocs but not with `name: windmill`:

```
theme:
  name: mkdocs
  highlightjs: true
  hljs_style: 'atelier-sulphurpool-light'
  hljs_languages:
    - protobuf
```