Underscores mess up code highlighting

[Michael-Geuenich]

Thanks for providing this package, I mainly use it to highlight my Rmarkdown code properly.

Unfortunately, it seems that the extension does not handle underscores well when they are in unquoted variable names in my Rmarkdown file (see image below).

When I have the extension enabled this is also an issue for any other scripts. For example, my python scripts then start looking like this whenever there is an underscore, which can become quite distracting.

[stibu81]

This also affects syntax highlighting in ordinary Python files, where no RMarkdown is involved.