Implement basic frontend-engine interaction

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

frontend/main.js

@@ -1,42 +1,24 @@
 import * as visuals from "./visuals.js";
 
-function setupBoard() {
-  let pawns = [];
-  for (let x of "abcdefgh") {
-    pawns.push(
-      new Piece("pawn", "black", `${x}7`),
-      new Piece("pawn", "white", `${x}2`)
-    );
-  }
-  return new Configuration([
-    new Piece("rook", "black", "a8"),
-    new Piece("rook", "black", "h8"),
-    new Piece("knight", "black", "b8"),
-    new Piece("knight", "black", "g8"),
-    new Piece("bishop", "black", "c8"),
-    new Piece("bishop", "black", "f8"),
-    new Piece("queen", "black", "d8"),
-    new Piece("king", "black", "e8"),
-
-    ...pawns,
-
-    new Piece("rook", "white", "a1"),
-    new Piece("rook", "white", "h1"),
-    new Piece("knight", "white", "b1"),
-    new Piece("knight", "white", "g1"),
-    new Piece("bishop", "white", "c1"),
-    new Piece("bishop", "white", "f1"),
-    new Piece("queen", "white", "d1"),
-    new Piece("king", "white", "e1"),
-  ]);
+function get_json(url) {
+  var request = new XMLHttpRequest();
+  request.open("get", url, false);
+  request.send(null);
+  return JSON.parse(request.responseText);
 }
 
 class Backend {
   constructor() {
-    this.config = setupBoard();
+    this.config = this.getConfig();
   }
   getConfig() {
-    return this.config.clone();
+    return new Configuration(
+      get_json("http://localhost:3000/get_state/").map((p) => {
+        let piece = new Piece();
+        Object.assign(piece, p);
+        return piece;
+      })
+    );
   }
   makeMove(move) {
     this.config = this.config.makeMove(move);