Single-quote strings

I'd love to use hil for a project but double-quotes are not very JSON friendly making the highlighting look all wonky, any chance of getting single-quoted strings in?

Start by locating HIL's string-literal parsing and related tests in the repository. Confirm the desired single-quoted syntax and its JSON-oriented highlighting behavior, then add coverage showing that single-quoted strings are accepted without changing existing double-quoted behavior. No files or tests are named in the issue, so repository exploration is required.

Written by the indexing model from the issue text.