this tool with take N binpacks as input to produce 1 binpack as output.
The input binpacks are read in random order, with a probability related to their size,
but each input file is read sequentially. The output is thus an appropriately shuffled binpack.
The tool is much faster than cat'ing the files together followed by a shuffle.
It assumes that the input binpacks themselves have no particular internal ordering.
in case a score can be parsed from the comment field in the pgn, add it to the output.
This form works for the fishtest pgns, and is quite common (cutechess-cli among others).
