Use chrono::duration for animation frame durations.

rand.cpp

@@ -3,4 +3,11 @@
 namespace Random {
   std::random_device RNG;
   std::mt19937 GENERATOR(RNG());
+
+
+  std::chrono::milliseconds milliseconds(int from, int to) {
+    int tick = Random::uniform_real(float(from), float(to));
+    return std::chrono::milliseconds{tick};
+  }
+
 }