Stan language support

[imadmali]

I love using this theme! Unfortunately, it doesn't support all of the variables in the Stan modeling language. From what I can tell, it's unable to highlight the variable declaration (int, vector, real, matrix, etc.) and the blocks (functions, data, parameters, model, generated quantities, etc.)

It would be great if you could fully support the language so that I can exclusively use An Old Hope.

Here's an example of what is looks like

And here's a comparison using Base16 Tomorrow Dark