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/opengl2_example/imgui_impl_glfw_gl2.cpp

@@ -249,7 +249,6 @@ bool    ImGui_ImplGlfwGL2_Init(GLFWwindow* window, bool install_callbacks)
 void ImGui_ImplGlfwGL2_Shutdown()
 {
     ImGui_ImplGlfwGL2_InvalidateDeviceObjects();
-    ImGui::Shutdown();
 }
 
 void ImGui_ImplGlfwGL2_NewFrame()