Big example binding refactor (manually imported from Viewport branch, stripped out of Viewport code). (#1870)

Read examples/README.txt for some details.
ImDrawData: Added DisplayPos, DisplaySize fields honored by all backends (not strictly necessary to honor just now, but doing it to be ahead)

examples/imgui_impl_dx11.h

@@ -0,0 +1,23 @@
+// ImGui Renderer for: DirectX11
+// This needs to be used along with a Platform Binding (e.g. Win32)
+
+// Implemented features:
+//  [X] User texture binding. Use 'ID3D11ShaderResourceView*' as ImTextureID. Read the FAQ about ImTextureID in imgui.cpp.
+//  [X] Multi-viewport rendering (when ImGuiConfigFlags_ViewportsEnable is enabled).
+
+// You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
+// If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().
+// If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
+// https://github.com/ocornut/imgui
+
+struct ID3D11Device;
+struct ID3D11DeviceContext;
+
+IMGUI_API bool        ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context);
+IMGUI_API void        ImGui_ImplDX11_Shutdown();
+IMGUI_API void        ImGui_ImplDX11_NewFrame();
+IMGUI_API void        ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data);
+
+// Use if you want to reset your rendering device without losing ImGui state.
+IMGUI_API void        ImGui_ImplDX11_InvalidateDeviceObjects();
+IMGUI_API bool        ImGui_ImplDX11_CreateDeviceObjects();