Document changes done to version 8.3.8-9.0.4

There has been good improvements to verion 8.3.8 (unfortunately I just couldn't catch up with all this in this situation), but I leave this to make sure I come back and document it all as needed.

The changes in this version can be found [HERE](https://swi-prolog.discourse.group/t/ann-swi-prolog-8-3-8/2983)