Changed callbacks to std::function

Now you can also use lambdas with captured values.

src/Application.hpp

@@ -12,10 +12,11 @@
 #include <SDL2/SDL.h>
 #include <map>
 #include <vector>
+#include <functional>
 
 namespace sc {
     namespace gui {
-        using EventHandler = bool(*)(const SDL_Event&);
+        using EventHandler = std::function<bool(const SDL_Event&)>;
         using RunLoopAction = void(*)();
 
         class Application {

src/Window.hpp

@@ -15,10 +15,11 @@
 #include <stdexcept>
 #include <vector>
 #include <map>
+#include <functional>
 
 namespace sc {
     namespace gui {
-        using WindowEventHandler = bool(*)(const SDL_Event&, bool quit);
+        using WindowEventHandler = std::function<bool(const SDL_Event&, bool quit)>;
         class Image;
 
         class Window {