Set C++ standard; code formatting.

On MacOS, clang will default to C++2003 if this isn't explicitly set.

CMakeLists.txt

@@ -1,6 +1,8 @@
 cmake_minimum_required(VERSION 3.22)
 
-project(kge)
+project(kge LANGUAGES CXX)
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 find_package(SDL2 REQUIRED)
 find_package(OpenGL REQUIRED)
@@ -23,28 +25,25 @@ add_library(imgui STATIC
         ext/imgui/backends/imgui_impl_opengl3.cpp
         ext/imgui/backends/imgui_impl_opengl3.h
 
-	ext/imgui/misc/freetype/imgui_freetype.cpp
-	ext/imgui/misc/freetype/imgui_freetype.h
-)
+        ext/imgui/misc/freetype/imgui_freetype.cpp
+        ext/imgui/misc/freetype/imgui_freetype.h)
 add_library(imgui::imgui ALIAS imgui)
 target_link_libraries(imgui
-    PUBLIC
-    OpenGL::GL
-    $<TARGET_NAME_IF_EXISTS:SDL2::SDL2main>
-    $<IF:$<TARGET_EXISTS:SDL2::SDL2>,SDL2::SDL2,SDL2::SDL2-static>
-    Freetype::Freetype
-)
+        PUBLIC
+        OpenGL::GL
+        $<TARGET_NAME_IF_EXISTS:SDL2::SDL2main>
+        $<IF:$<TARGET_EXISTS:SDL2::SDL2>,SDL2::SDL2,SDL2::SDL2-static>
+        Freetype::Freetype)
 target_include_directories(imgui PUBLIC
-	ext/imgui/
-	ext/imgui/backends/
-	ext/imgui/misc/freetype
-	${FREETYPE_INCLUDE_DIRS}
-)
+        ext/imgui/
+        ext/imgui/backends/
+        ext/imgui/misc/freetype
+        ${FREETYPE_INCLUDE_DIRS})
 
-include_directories(ext/)
+include_directories(ext/ ${SDL2_INCLUDE_DIRS})
 
 add_executable(kge
-	kge.cc
-)
+        kge.cc
+		)
 target_link_libraries(kge imgui)