Feature request: Ability to see formatted/rendered preview

:bulb: The Idea

We use this library a bunch to deliver Slack messages. However, formatting is always tricky and we often get formatting rules wrong a few times before getting it right. Any interest in a "test", "preview" or "render" interface that would (in our case), render a preview of the Slack message in markdown or html or similar?

:hammer: Breaking Feature

Nothing breaking.

❗ Hard Part

Goes without saying that supporting n preview engines could get unwieldy. Perhaps those could be added as their own targets? Like slack-html-preview could be a separate engine to use when wanting a preview of what slack would deliver.

Other solutions might be available - just wanted to put the idea out there and see if it's interesting and/or possible.