Loser Tree data structure, for fast k-way merge

I will be speaking about this at GopherCon on 27th Sept 2023.

There are currently two versions of the code on two Git branches: main, which works for built-in types like int and string, and any which works on any type but requires you to pass in a function pointer to do less comparisons.

See https://en.wikipedia.org/wiki/K-way_merge_algorithm#Tournament_Tree for more details on the algorithm.