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.

examples/allegro5_example/main.cpp

@@ -23,6 +23,7 @@ int main(int, char**)
     al_register_event_source(queue, al_get_mouse_event_source());
 
     // Setup ImGui binding
+    ImGui::CreateContext();
     ImGuiIO& io = ImGui::GetIO(); (void)io;
     ImGui_ImplA5_Init(display);
     //io.NavFlags |= ImGuiNavFlags_EnableKeyboard;  // Enable Keyboard Controls
@@ -118,6 +119,7 @@ int main(int, char**)
 
     // Cleanup
     ImGui_ImplA5_Shutdown();
+    ImGui::DestroyContext();
     al_destroy_event_queue(queue);
     al_destroy_display(display);