ENH: Support all Scipy window types in rolling(..., win_type)
- [x] closes #34556
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Additionally cleans up some helper methods
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 2020-10-30 19:32:34 UTC All green besides the (expected) failing 32-bit build thanks @mroeschke 