LU Decomposition - return permutation matrix instead of vector

[dpsanders]

julia> p = [2, 1, 3];

julia> n = length(p);

julia> II = Matrix{Int}(I, n, n)
3×3 Array{Int64,2}:
 1  0  0
 0  1  0
 0  0  1

julia> II[p, :]
3×3 Array{Int64,2}:
 0  1  0
 1  0  0
 0  0  1