Rolling Apply Docs Broken
A google of "rolling apply" for me yields:

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.window.Rolling.apply.html

Which results in an HTTP 403. Working link now is:

https://pandas.pydata.org/docs/reference/api/pandas.core.window.rolling.Rolling.apply.html

As pointed out by @TomAugspurger seems to be an issue with `window.Rolling.apply` vs `window.rolling.Rolling.apply` (/docs should be a symlink to /pandas-docs/stable)