Add vignette demonstrating converting old syntax

[jgabry]

We need to remove the Deprecations vignette because it no longer applies with version 2.33 (see #843 (comment)), but we should add a vignette demonstrating converting old syntax.

[jgabry]

Maybe we don't actually need this if we have #852? On that branch the doc for the format method shows how to do this and updates the error message to point to that doc.