rename engine.hpp/cpp to Engine.hpp/cpp & move Engine, Time and mainloop classes to 'engine' folder

src/frontend/debug_panel.cpp

@@ -1,6 +1,6 @@
 #include "audio/audio.hpp"
 #include "delegates.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "settings.hpp"
 #include "hud.hpp"
 #include "content/Content.hpp"

src/frontend/hud.cpp

@@ -8,7 +8,7 @@
 #include "content/Content.hpp"
 #include "core_defs.hpp"
 #include "delegates.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "graphics/core/Atlas.hpp"
 #include "graphics/core/Batch2D.hpp"
 #include "graphics/core/Batch3D.hpp"

src/frontend/menu.cpp

@@ -5,7 +5,7 @@
 #include "screens/MenuScreen.hpp"
 
 #include "delegates.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "data/dv.hpp"
 #include "interfaces/Task.hpp"
 #include "files/engine_paths.hpp"

src/frontend/screens/LevelScreen.cpp

@@ -5,7 +5,7 @@
 #include "content/Content.hpp"
 #include "core_defs.hpp"
 #include "debug/Logger.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "files/files.hpp"
 #include "frontend/LevelFrontend.hpp"
 #include "frontend/hud.hpp"

src/frontend/screens/MenuScreen.cpp

@@ -8,7 +8,7 @@
 #include "maths/UVRegion.hpp"
 #include "window/Window.hpp"
 #include "window/Camera.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 
 MenuScreen::MenuScreen(Engine& engine) : Screen(engine) {
     engine.resetContent();

src/frontend/screens/Screen.cpp

@@ -1,7 +1,7 @@
 #include "Screen.hpp"
 
 #include "graphics/core/Batch2D.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 
 Screen::Screen(Engine& engine)
   : engine(engine),