Add interpolation options to rolling quantile
It version 0.21.0 rolling quantile started to use linear interpolation, it broke backward compatibility.

Regular (not rolling) quantile supports these interpolation options: `linear`, `lower`, `higher`, `nearest` and `midpoint`.
This commit adds the same options to moving quantile.

Performance issues of this commit (note: I re-run benchmarks, see message below) 
This code has 15% worse performance on benchmarks with small values of window (`window=10`). This is because loop inside `roll_quantile` now contains switch.
I tried to replace switch with callback but it led to even worse performance. Even if I move some of the code to new function (without any change in logic) it still makes performance much worse.
How bad is it? Could you please give me an advice on how to arrange the code such that it has the same performance?

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
