Roll apply nonfloat dtypes

[sandhujasmine]

Fixed issue #4964 so rolling_apply works on non-numeric columns as well.

I followed instructions here but I'm not sure where to add documentation in the release notes.

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

[jreback]

this would be after #11603

but you don't actually want to modify roll_generic, rather you want to have different functions for different dtypes based on there input. So would need to modify the templates to generate object ones (which is prob useful), otherwise coerce to float.

[sandhujasmine]

Are the #11603 changes already in master?

I thought about creating a different rolling_* function for each dtype but the logic would be almost identical to rolling_generic() with changes in the dtype of input and a couple of dtype changes in the function.

It seemed cleaner (and DRY) to always give it a float as 'input' and give it another numpy array called array_to_roll when we have a non-float type we wish to roll over. Are you concerned about performance? I was unsure if coercion should be exposed to user and if it should default to True, but optimized for speed - anyhow, moot points if that's not the route we wish to go.

But curious if you prefer different but almost identical functions to roll_generic for each non float dtype. I can certainly give this a go in another branch, and we can see how similar the functions are then discuss further.

[jreback]

@sandhujasmine we use template generation to handle the differnt dtypes, see src/generate_code.pyx. you would end up with roll_generic_float64 and roll_generic_object. These refer to the input types (you can also use a fused type for this, look for the numeric type). but we usually have a separate routine for object as well, as it sometimes needs customization.
further its possible to have a matrixed set of input/output types (but I don't really like this), and would instead assert that the input type produces the same output type (and if it doesn't then it would raise and we would just use the roll_generic_object anyhow.