Provide links for older version (draft-4, ...)

[evaisse]

Is That possible to provide a link to Jekyll some branches of this repo ?
Something like pointing over a branche feature/draft-4 ? :

https://draft-4.json-schema.org/understanding-json-schema/

But maybe this issue should be more related to json-schema.org ?
In any case, I don't see any version tag or branches to do such a fix.

Thanks, great job for this doc anyway.

[mdboom]

The idea is actually to make it clear in the text when certain features became available so you can use the same document to target different versions (much like how the Python documentation does this).