Update _core.py with missing parameters
added missing parameters:
 - ax
 - subplots
 - sharex
 - sharey
 - secondary_y
 - sort_columns
 - stacked

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @loudlemon! 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 2020-05-03 03:42:43 UTC Not super well versed in this area so @datapythonista merge when happy Thanks @loudlemon 