Merge branch 'master' into docking

# Conflicts:
#	backends/imgui_impl_metal.mm
#	backends/imgui_impl_opengl3.cpp
#	backends/imgui_impl_osx.mm
#	backends/imgui_impl_win32.cpp
#	docs/CHANGELOG.txt

backends/imgui_impl_sdl2.cpp

@@ -552,6 +552,7 @@ void ImGui_ImplSDL2_Shutdown()
 
     io.BackendPlatformName = nullptr;
     io.BackendPlatformUserData = nullptr;
+    io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos | ImGuiBackendFlags_HasGamepad);
     IM_DELETE(bd);
 }