Add one killer move per ply

src/board/fen.rs

@@ -2,7 +2,7 @@ use crate::board::board::{Board, Color, PieceType};
 use crate::board::game::Game;
 use crate::board::state::{Castle, State};
 use crate::search::transposition_table::TranspositionTable;
-use crate::search::MAX_TT_SIZE;
+use crate::search::{MAX_DEPTH, MAX_TT_SIZE};
 use String as FenError;
 
 pub fn from_fen(fen: &str) -> Result<Game, FenError> {
@@ -37,6 +37,7 @@ pub fn from_fen(fen: &str) -> Result<Game, FenError> {
         mailbox,
         hash,
         tt: TranspositionTable::new(MAX_TT_SIZE),
+        killer: [None; MAX_DEPTH as usize],
     })
 }