Refactor messaging to use runtime port API

[averycrespi]

Docs: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/Runtime/Port

• Change roll20.js and background.js
• Update "how the extension works" docs

[Slavanich]

sorry to ask but is vtt bridge still down? can't get it to connect with dmv.

[averycrespi]

Hi @Slavanich ! VTT Bridge should be fully functional.

Please file a bug report, and I'll investigate further.

EDIT: You can also check your extension version in about:addons (Firefox) or chrome://extensions (Chrome). If you're still running v1.2.0, you'll need to update.