Small clean-ups

- Comment for Countemove pruning -> Continuation history
- Fix comment in input_slice.h
- Shorter lines in Makefile
- Comment for scale factor
- Fix comment for pinners in see_ge()
- Change Thread.id() signature to size_t
- Trailing space in reprosearch.sh
- Add Douglas Matos Gomes to the AUTHORS file
- Introduce comment for undo_null_move()
- Use Stockfish coding style for export_net()
- Change date in AUTHORS file

closes https://github.com/official-stockfish/Stockfish/pull/3416

No functional change

src/search.cpp

@@ -862,7 +862,6 @@ namespace {
              && ttValue != VALUE_NONE
              && ttValue < probCutBeta))
     {
-
         assert(probCutBeta < VALUE_INFINITE);
 
         MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
@@ -1025,7 +1024,7 @@ moves_loop: // When in check, search starts from here
           }
           else
           {
-              // Countermoves based pruning (~20 Elo)
+              // Continuation history based pruning (~20 Elo)
               if (   lmrDepth < 4
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
                   && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
@@ -1528,7 +1527,7 @@ moves_loop: // When in check, search starts from here
                                                                 [pos.moved_piece(move)]
                                                                 [to_sq(move)];
 
-      // CounterMove based pruning
+      // Continuation history based pruning
       if (  !captureOrPromotion
           && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold