mark _unused fields as such, don't bind unused vars in match

src/arena.rs

@@ -11,10 +11,10 @@ use tile::Tile;
 // 0x40   121  11x11 map matrix
 // 0xB9   7    ???
 pub struct Arena {
-  monster_x: [u8; 16],
-  monster_y: [u8; 16],
-  party_x: [u8; 8],
-  party_y: [u8; 8],
+  _monster_x: [u8; 16],
+  _monster_y: [u8; 16],
+  _party_x: [u8; 8],
+  _party_y: [u8; 8],
   _unknown1: [u8; 16],
   map: Field,
   _unknown2: [u8; 7],