Thread history

Because the different halves of each pairing are stored separately, each might have a slightly different idea of what its score is against each other because one of the scores being dropped from cache before it is written to disk. Now that I'm not trying to complete pairings for Melee and Roborumble I might as well reduce the caching to less dangerous levels. I've also considered fixing this in my batch processing by taking averages, but never got around to it.