The suite should explicitly document its backwards compatibility policy

This suite is generally not versioned (despite such things having been requested in the past).

Regardless though, it is important to define exactly what sorts of backwards compatibility we offer. E.g. -- do we guarantee that files will stay in the same location? That tests will not change descriptions? That the directory structure won't change?

Some of these things have changed recently, so to help those who use the suite, we should explicitly note which of the above (and others) we guarantee.

Possibly here we should also therefore change the structure of the repo into one that clearly delineates between an authoring format and an output format -- e.g., from an authoring standpoint, it's potentially annoying to have to replicate tests across drafts, so perhaps tests should by default be replicated, unless explicitly restricted. But from an output standpoint, it's likely more convenient to fully denormalize the output, so that users of the suite can treat each version completely independently.