add basic save and load

add menu
- save
- load
- demo on/off
- close + popup

#9 #10

src/main_linux.cpp

@@ -349,6 +349,9 @@ static void FramePresent(ImGui_ImplVulkanH_Window* wd)
     wd->SemaphoreIndex = (wd->SemaphoreIndex + 1) % wd->SemaphoreCount; // Now we can use the next set of semaphores
 }
 
+bool should_exit = false;
+bool show_demo_window = false;
+
 // Main code
 int main(int, char**)
 {
@@ -443,7 +446,6 @@ int main(int, char**)
     //IM_ASSERT(font != nullptr);
 
     // Our state
-    bool show_demo_window = true;
     bool show_another_window = false;
     ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);