Merge NNUE (master) in the cluster branch.

fixes minor merge conflicts, and a first quick testing looks OK:

4mpix4th vs 4th at 30+0.3s:

Score of cluster vs master: 3 - 0 - 37  [0.537] 40
Elo difference: 26.1 +/- 28.5, LOS: 95.8 %, DrawRatio: 92.5 %

No functional change.

src/main.cpp

@@ -1,8 +1,6 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
-  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
-  Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+  Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -48,6 +46,7 @@ int main(int argc, char* argv[]) {
   Endgames::init();
   Threads.set(size_t(Options["Threads"]));
   Search::clear(); // After threads are up
+  Eval::init_NNUE();
 
   UCI::loop(argc, argv);