Make Array sortable or document "how" to do it

Hello,

I have been unable to deduce how to "correctly" use `std.algorithm.sort` on an Array!T. A quick and dirty solution that I managed to make work where to expose _payload and use that directly.

But after I did that, ohh my, did Array work nice. I like it! Changing a from dynamic slices to Array and the GC pressure more than halved.

Regards, Joakim

