Syntax highlighting does not respect language specified

In the windmill theme, try writing a page containing the following code block:

````
```sh
git clone https://github.com/gristlabs/mkdocs-windmill.git
```
````

It will ignore the language specification and attempt to guess the language instead, probably arriving at some conclusion like "vim" and highlighting the `s:` in the URL blue (!).

For two years, mkdocs [has supported disabling highlight.js](https://github.com/mkdocs/mkdocs/issues/467#issuecomment-402824455), which is great because highlight.js insists on guessing the code language, ignoring the user's explicit direction, and guesses something silly, as in the example above. In all built-in mkdocs themes, you can do:

```
theme:
highlightjs: false

markdown_extensions:
- codehilite

extra_css:
- css/code_styles.css
```

Please add support for this to windmill.

To see how mkdocs did it for their themes, check out, for example, [this PR](https://github.com/mkdocs/mkdocs/pull/1533/files#diff-6a7c9a590efa5c4589e669f54ad36bc9).

Thanks!