Simplify evaluation

This is more work from the just_elo_change branch.  I've tested this change against master at 10+1, and will continue doing so, but it's looking good after 5900 games:

ELO: 5.52  +- 99%: 11.66 95%: 8.86
LOS: 98.77%
Wins: 921 Losses: 827 Draws: 4172