feat: add localStorage highscore module

scores.js

@@ -0,0 +1,9 @@
+function getHighscore(game) {
+  return parseInt(localStorage.getItem('hs_' + game) || '0', 10);
+}
+
+function setHighscore(game, score) {
+  if (score > getHighscore(game)) {
+    localStorage.setItem('hs_' + game, score);
+  }
+}