Add Zobrist hashing

src/board/fen.rs

@@ -27,11 +27,13 @@ pub fn from_fen(fen: &str) -> Result<Game, FenError> {
     ));
 
     let mailbox = Mailbox::new_from_board(&board);
+    let hash = zobrist_keys().calculate_hash(&board);
 
     Ok(Game {
         board,
         history: History::new(),
         mailbox,
+        hash,
     })
 }
 
@@ -132,6 +134,7 @@ use std::collections::HashMap;
 
 use super::history::History;
 use super::mailbox::Mailbox;
+use super::zobrist::zobrist_keys;
 
 fn en_passant_square(square: &str) -> Result<Option<usize>, FenError> {
     let mut sqr = square.chars();