ENH: Use Kahan summation and Welfords method to calculate rolling var and std
- [x] xref #37051
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

As suggested by @mroeschke Kahan summation fixes the numerical problems. Additionally I used Welfords Method to calculate ``ssqdm``, because previously the tests I have added would return

```
0             NaN
1    3.500000e+34
2    3.000000e+34
3    3.000000e+34
4    3.000000e+34
5    3.000000e+34
6    3.000000e+34
7    3.000000e+34
8    3.000000e+34
9    3.000000e+34
dtype: float64
```

for ``var()``. I am running the asv and will post the results when available