ERR: Raise NotImplementedError with BaseIndexer and certain rolling operations
- [x] xref #32865
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

As a temporary solution for returning incorrect results when using a BaseIndexer subclass with certain rolling operations, a `NotImplementedError` will now raise with instructions to use `apply` instead.
Hello @mroeschke! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:







There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-03-28 20:52:23 UTC thanks @mroeschke 