[WIP] Sparse output KNN

WIP in early stages

- [x] Implement Cython CSR rowise mode function in sparsefuncs_fast
- [ ] Implement Cython CSR rowise weighted_mode function in sparsefuncs_fast
I see, I bench marked this Cython function vs python code of the same implementation and it preformed the same. The next step will be to do this calculation with Cython code.