decoupled timers from interpreter tick rate

CountdownTimerSDL.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <SDL2/SDL_timer.h>
+
+#include "Peripherals.hpp"
+
+class CountdownTimerSDL : public chocochip8::CountdownTimer {
+public:
+  CountdownTimerSDL(unsigned frequency); 
+  void set(unsigned value) override;
+  unsigned get() const override;
+private:
+  const Uint64 mDesiredFrequency;
+  const Uint64 mSDLFrequency;
+  Uint64 mStartTime;
+  Uint64 mStartValue;
+};