ENH: Negative Reference Percent Changes
- [x] closes #xxxx
- [ ] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

I recently came across a problem at work that looks like it should be solved in `pct_change`. To make the problem apperent, here is a quote from the [relative change and difference Wikipedia page](https://en.wikipedia.org/wiki/Relative_change_and_difference#Definitions):
> If we are calibrating a thermometer which reads −6 °C when it should read −10 °C, this formula for relative change (which would be called relative error in this application) gives ((−6) − (−10)) / (−10) = 4 / −10 = −0.4, yet the reading is too high To fix this problem we alter the definition of relative change so that it works correctly for all nonzero values of x<sub>reference</sub>:
![alt text](https://wikimedia.org/api/rest_v1/media/math/render/svg/5c819461a566c88ed96dc839638581a875c7fe31)

The example I list in the updated docstrings is also a good example:
> -10 -> 10

Clearly it seems weird to say that the pct change is -200% for this. Dividing by the abs of the reference value fixes this to +200%.