rank revealing Cholesky decomposition
add the changes made in https://github.com/pachadotdev/armadillo/commit/ea943daca8bbb075218dbf2ed928d2c84bf6b17f#diff-834bfe2cc2959ef8506cc9f3c7aa28c939c638d039285979dae743df4bec81b5
I tested this function here: https://github.com/pachadotdev/armadillo/commit/ea943daca8bbb075218dbf2ed928d2c84bf6b17f#diff-51920e95310ebfbc1ae31709f3b95f89afffbf4f1a6e38e8b2b406e2fb6197ea
From GitHub, I only added the changed to fn_chol.hpp.