DOC: small whatsnew updates
this may not be exactly correct from a doc perspective (and prob adds some warnings), but getting the data in the right place for now. A bit late (could also keep such things open a bit longer), but:

- I would for now not add more classes to the api.rst until we figure out the api issues (how to not add all its members), so the task to fix that does not become larger
- in general when adding things to api.rst, we should make sure they have actually docstrings. Now almost all the classes added have empty pages. right this was mainly to get things started 