feature/combat rating system

util/combatRatingHandler.js

@@ -0,0 +1,6 @@
+module.exports = {
+  calculateNewCombatRating: (Ra, Rb, score) => {
+    const Ea = 1 / (1 + Math.pow(10, ((Rb - Ra) / 400)));
+    return Math.round(Ra + 32 * (score - Ea));
+  },
+}