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_vulkan.cpp

@@ -1051,6 +1051,7 @@ void ImGui_ImplVulkan_Shutdown()
 
     io.BackendRendererName = nullptr;
     io.BackendRendererUserData = nullptr;
+    io.BackendFlags &= ~ImGuiBackendFlags_RendererHasVtxOffset;
     IM_DELETE(bd);
 }