Roll apply nonfloat dtypes
Fixed issue [#4964](https://github.com/pydata/pandas/issues/4964) so rolling_apply works on non-numeric columns as well.

I followed instructions [here](https://github.com/pydata/pandas/blob/master/CONTRIBUTING.md) but I'm not sure where to add documentation in the [release notes](https://github.com/pydata/pandas/blob/master/CONTRIBUTING.md#documenting-your-code). 

Also would like to get feedback on the code and complete any code changes before adding to documentation.
