Undocumented Breaking Changes for 9.0.0

[ahilke]

I was looking at the project and got confused around version 9.

Firstly, the release does not mention any breaking changes, but as far as I can tell it actually dropped support for Node 14 and 16 based on this PR: #309. It would be very beneficial to provide a list of breaking changes with major releases to help with upgrading.

Secondly, I believe with the release of version 9 a few issues that referred to an upcoming version 9 are outdated, for example #299.
It might make sense to go through them and close or update them as required.

[mcollina]

Thanks for the feedback