Switch to actively maintained 3rd party parser package

[sebastiaanspeck]

jison, which we currently use for the parser, is not actively maintained anymore (last commit 5 years ago) and it has an outdated dependency (npm warn deprecated nomnom@1.5.2: Package no longer supported. Contact support@npmjs.com for more info.)

[owenvoke]

I've previously looked into finding a maintained parser package with no luck for what we were using it for (and most seemed to not be maintained). I'd be interested if we can find one now though. 👍🏻

Some I had found before were nearley and PEG.js, but both hadn't been updated for years.

There is a successor to PEG.js called peggy, which seems to be maintained.