Update Armadillo to 4.000.0

	
Version 4.000   (Feral Steamroller)
added eigen decompositions of sparse matrices: eigs_sym() and eigs_gen()
added eigen decomposition for pair of matrices: eig_pair()
added simpler forms of eig_gen()
added condition number of matrices: cond()
expanded find() to handle cubes
expanded subcube views to access elements specified in a vector
template argument for running_stat_vec expanded to accept vector types
more robust fast inverse of 4x4 matrices
faster divide-and-conquer decompositions are now used by default for eig_sym(), pinv(), princomp(), rank(), svd(), svd_econ()
the form inv(sympd(X)) no longer assumes that X is positive definite; use inv_sympd() instead
added MEX connector for interfacing Octave/Matlab with Armadillo matrices (contributed by George Yammine)