Suggestion: Add nimlime style highlighting for template macros

[onionhammer]

I'm obviously biased here, and this is not part of the language, but I am gauging interest in implementing this feature; i.e. if implement it, would you/all be interested in merging it?

Currently if you do simple highlighting like this:

const value = tmpl html"""
     <div>Item is $item</div>
"""

The string doesn't highlight as HTML in vscode-nim