Suggestion: Add Markdown quote Languages

[RandomnessRobin]

I tried code today, And I really enjoyed using it but as I was in the markdown(.md) file I tried to do a js quote with

```js 
const pizza = [cheese, bread, salsa, toppings"]
>```

When I was using VS Code, doing this would change the colors according to what it is with JavaScript, for example. This is it. Thank you for all the hard work & dedication for the app.

[jeremypw]

Not sure the Gtk.SourceBuffer we use supports this. As far as I can see, there is a "language" property of the whole buffer which governs the syntax highlighting, and only one buffer per document. There is no obvious way of applying a different language property to a section of text.