Use correct chess terms + fix spelling.

- "discovered check" (instead of "discovery check")
  - "en passant" (instead of "en-passant")
  - "pseudo-legal" before a noun (instead of "pseudo legal")
  - "3-fold" (instead of "3fold")

closes https://github.com/official-stockfish/Stockfish/pull/3294

No functional change.

src/types.h

@@ -113,7 +113,7 @@ constexpr int MAX_PLY   = 246;
 /// bit  6-11: origin square (from 0 to 63)
 /// bit 12-13: promotion piece type - 2 (from KNIGHT-2 to QUEEN-2)
 /// bit 14-15: special move flag: promotion (1), en passant (2), castling (3)
-/// NOTE: EN-PASSANT bit is set only when a pawn can be captured
+/// NOTE: en passant bit is set only when a pawn can be captured
 ///
 /// Special cases are MOVE_NONE and MOVE_NULL. We can sneak these in because in
 /// any normal move destination square is always different from origin square
@@ -127,7 +127,7 @@ enum Move : int {
 enum MoveType {
   NORMAL,
   PROMOTION = 1 << 14,
-  ENPASSANT = 2 << 14,
+  EN_PASSANT = 2 << 14,
   CASTLING  = 3 << 14
 };