Log Message:
math/R-RcppArmadillo: Update to 0.8.400.0.0

Changes:
    - faster handling of sparse matrices by repmat()
    - faster loading of CSV files
    - expanded kron() to handle sparse matrices
    - expanded index_min() and index_max() to handle cubes
    - expanded randi(), randu(), randn(), randg() to output single scalars
    - added submatrix & subcube iterators
    - added normcdf()
    - added mvnrnd()
    - added chi2rnd()
    - added wishrnd() and iwishrnd()