As part of our ongoing effort to make the runtimes more awesome, we have introduced a separate change log detailing API changes, API additions as well as otherwise important changes to each runtime. You can find the current change log for the 3.6-beta development branch at spine-runtimes/CHANGELOG.md at 3.6-beta
I'd be happy to get feedback on the change log format. It's current structure is
VERSION
* language
* language change
* [engine]
* engine change