Merge branch 'context'

# Conflicts:
#	examples/allegro5_example/main.cpp
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx9_example/main.cpp
#	examples/marmalade_example/main.cpp
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

examples/vulkan_example/imgui_impl_glfw_vulkan.cpp

@@ -789,7 +789,6 @@ bool    ImGui_ImplGlfwVulkan_Init(GLFWwindow* window, bool install_callbacks, Im
 void ImGui_ImplGlfwVulkan_Shutdown()
 {
     ImGui_ImplGlfwVulkan_InvalidateDeviceObjects();
-    ImGui::Shutdown();
 }
 
 void ImGui_ImplGlfwVulkan_NewFrame()

examples/vulkan_example/main.cpp

@@ -614,6 +614,7 @@ int main(int, char**)
     setup_vulkan(window);
 
     // Setup ImGui binding
+    ImGui::CreateContext();
     ImGuiIO& io = ImGui::GetIO(); (void)io;
     ImGui_ImplGlfwVulkan_Init_Data init_data = {};
     init_data.allocator = g_Allocator;
@@ -745,6 +746,7 @@ int main(int, char**)
     VkResult err = vkDeviceWaitIdle(g_Device);
     check_vk_result(err);
     ImGui_ImplGlfwVulkan_Shutdown();
+    ImGui::DestroyContext();
     cleanup_vulkan();
     glfwTerminate();