make game update function pure virtual, add Animation class to sb namespace

src/Animation.hpp

@@ -68,4 +68,12 @@ public:
 
 };
 
+/* Add Animation class to the sb namespace. This should be the default location, but Animation is left in the global namespace
+ * for backward compatibility.
+ */
+namespace sb
+{
+    using ::Animation;
+}
+
 #include "Node.hpp"

src/Game.hpp

@@ -62,7 +62,6 @@ protected:
 
 private:
 
-    int ticks;
     float frame_length = 1000.0 / 60.0;
     SDL_Window* _window;
     std::shared_ptr<TTF_Font> _font;
@@ -151,7 +150,7 @@ public:
     void run();
     void frame(float);
     void flag_to_end();
-    virtual void update(float timestamp) {};
+    virtual void update(float timestamp) = 0;
     void set_framerate(int);
     float get_frame_length() const;
     void handle_quit_event(SDL_Event&);

src/Timer.hpp

@@ -23,7 +23,7 @@ namespace sb
     private:
 
         bool timing = false, previous_is_recorded = false;
-        float timestamp = 0.0f, timestamp_previous = 0.0f, frame_duration = 0.0f, _elapsed = 0.0f;
+        float timestamp_previous = 0.0f, frame_duration = 0.0f, _elapsed = 0.0f;
 
     public: