SFML: set default window size to 640x480

platform/sfml/Graphics.cpp

@@ -12,7 +12,7 @@ sf::RenderTexture buffer;
 
 void GRAPHICS::init()
 {
-    window.create(sf::VideoMode(320, 240), "WalrusRPG");
+    window.create(sf::VideoMode(640, 480), "WalrusRPG");
     view = sf::View(window.getDefaultView());
     buffer.create(320, 240);
 }