Spearman's rank correlation for rowCorCpp

[RegnerM2015]

Hi @rcorces and @jeffmgranja ,

To my understanding, rowCorCpp is responsible for computing Pearson correlations for peak-to-gene correlations and for peak co-accessibility.

I was wondering if it would be possible to implement an option for computing Spearman correlations in addition to Pearson correlations?

We could implement the Spearman correlation formula here:
https://github.com/GreenleafLab/ArchR/blob/f6c0388bd37023400794c9ae8562ad69e3ba9fd7/src/Correlation.cpp

I am not familiar with C++ so I wanted to reach out and ask if this was a feasible option.