How to sort a multidimensional ndslice?

[Arredondo]

I want to sort a two-dimensional ndslice by its columns according 
to some predefined predicate.

What I mean is _not_ sorting the contents of each column 
individually, but instead to reorder the entire columns of the 
matrix so that they are sorted according to some "greater than" 
function.

Here's a MWE (the `larger` function is just an example):

```
import std.stdio;

import mir.ndslice.slice;
import mir.ndslice.sorting;

void main() {
     auto a = [[1, -1, 3, 2],
               [0, -2, 3, 1]].sliced;

     writeln(a);
     a.byDim!1.sort!((u, v) => larger(u, v));
     writeln(a);
}

auto larger(C)(C u, C v) {
     import mir.math.sum : sum;
     return sum(u) > sum(v);
}
```

I would have expected this to print:
[[1, -1, 3, 2], [0, -2, 3, 1]]
[[3, 2, 1, -1], [3, 1, 0, -2]]

but instead it prints
[[1, -1, 3, 2], [0, -2, 3, 1]]
[[1, -1, 3, 2], [0, -2, 3, 1]]

i.e, nothing happens!
Any suggestions?

Arredondo.