biased (dbcn) and known from human master play

Opening book for fishtesting containing 198350 lines, biased and known from human master play. Each line has at most eight full moves (commencing always from the default starting position). 88192 of the lines have at most six full moves, 19424 have at most four full moves and 1286 have at most two full moves. 154148 lines have advantage for white and 44202 have advantage for black. The side that is first to move is the side that has the advantage. The bias (according to dbcn on about 2021-07-19) is distributed as follows: 40cp<=bias<60cp, 47633 cases. 60cp<=bias<80cp, 36462 cases. 80cp<=bias<100cp, 48859 cases. 100cp<=bias<120cp, 37279 cases. 120cp<=bias<140cp, 28117 cases. Openings are distributed as follows: 1. e4, 92647 cases (1. e4 c5, 30183 cases; 1. e4 e5, 20998 cases; 1. e4 e6, 12398 cases, ...); 1. d4, 68815 cases (1. d4 Nf6, 45648 cases; 1. d4 d5, 11793 cases; ...); 1. Nf3, 1. c4 and all other, 36888 cases. The order of lines has been randomized, but the order is preserved between the pgn and the epd version of the book. Further discussion on the Stockfish resources-general-info Discord channel around 2021-07-19; background data on http://chessopeningsforengines.wikidot.com/.

closes #18