Determinant

[JohannesEngels]

A suggestion for src/arraymancer/linear_algebra/decomposition.nim: Seems that the computation of the determinant of a matrix is missing so far. It could be easily achieved by means of the LU-decomposition, as the determinant is just the product of the diagonal elements of the matrix U - up to the sign! Therefore it would be very helpful to give out also the number of permutations or at least the pivot_indices vector. (Of course I am talking about proc lu_permuted; in the current stage it is a bit cumbersome to determine the number of permutations from the output.)

[Vindaar]

That would certainly be a useful addition. Do you feel like taking a stab at implementing it?