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/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

@@ -361,7 +361,6 @@ bool    ImGui_ImplSdlGL3_Init(SDL_Window* window)
 void ImGui_ImplSdlGL3_Shutdown()
 {
     ImGui_ImplSdlGL3_InvalidateDeviceObjects();
-    ImGui::Shutdown();
 }
 
 void ImGui_ImplSdlGL3_NewFrame(SDL_Window* window)