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/allegro5_example/imgui_impl_a5.cpp

@@ -201,7 +201,6 @@ bool ImGui_ImplA5_Init(ALLEGRO_DISPLAY* display)
 void ImGui_ImplA5_Shutdown()
 {
     ImGui_ImplA5_InvalidateDeviceObjects();
-    ImGui::Shutdown();
 }
 
 // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.