Application: Unblocked LU Factorization

LU factorization with pivoting

Implement the LU factorization with pivoting:

Solve your example problem with pencil and paper
Change your factorization such that it also handles pivoting. Implement for this the following BLAS functions as auxiliary tools:
- Write a function dswap for interchanging values of two vectors:
```
void
dswap(size_t n, double *x, ptrdiff_t incX, double *y, ptrdiff_t incY)
{
    // Your code
}
```
- Write a function idamx that returns for a vector the index with maximal absolute value:
```
size_t
idamax(size_t n, const double *x, ptrdiff_t incX)
{
    // Your code
}
```
Change main such that it also prints the pivot vector after the factorization.