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
