VSCode embedded language support in Markdown

Allow DF Raw syntax highlighting in DF Raw markdown blocks.

For example:

# Title
This is a **markdown** file.

```df_raw
descriptor_color_standard

[OBJECT:DESCRIPTOR_COLOR]

[COLOR:AMBER]
    [NAME:amber]
    [WORD:AMBER]
    [RGB:255:191:0]
```

This would only work when the file is opened in VSCode, not when viewed in GitLab. But this would still be an improvement.

To help created this: