How can I add a custom grammar to the linter

[zenopopovici]

Hello,

We've recently switched to nunjucks by mozilla and it's a pain without htmlhint.
Is there a way to add a custom grammar to the linter? If we change the file type to HTML linting works perfectly.

Thanks

[zenopopovici]

I see we could just update the GRAMMAR_SCOPES array with text.html.nunjucks.

Maybe we could have a preference pane for dealing with grammars?

[Arcanemagus]

This is somewhat a duplicate of #82, but this is a solution to that that is easy enough to implement. As soon as the CI issues are sorted out I can throw a PR up that fixes this.