Implement basic frontend-engine interaction

Use a Flask-based Python server as an adapter to the engine's
stdin-stdout inferface.

rs/src/board.rs

@@ -224,15 +224,17 @@ impl Board {
         };
     }
     pub fn new() -> Board {
-        let mut board = Board {
+        Board {
             state: Default::default(),
-        };
+        }
+    }
+    pub fn reset(&mut self) {
+        self.state.clear();
         for piece_type in &[PieceType::Pawn] {
             for (piece, position) in piece_type.initial_setup() {
-                board.set_at(position, Some(piece));
+                self.set_at(position, Some(piece));
             }
         }
-        board
     }
     pub fn iter(&self) -> impl Iterator<Item = (&Position, &Piece)> {
         self.state.iter()