Merge branch 'master' into docking

# Conflicts:
#	backends/imgui_impl_dx10.cpp
#	backends/imgui_impl_dx11.cpp
#	backends/imgui_impl_dx12.cpp
#	backends/imgui_impl_dx9.cpp
#	backends/imgui_impl_opengl3.cpp
#	backends/imgui_impl_win32.cpp
#	docs/CHANGELOG.txt
#	examples/example_glfw_vulkan/main.cpp
#	examples/example_sdl_vulkan/main.cpp
#	imgui.cpp

examples/example_apple_opengl2/main.mm

@@ -97,7 +97,7 @@
     GLsizei height = (GLsizei)(draw_data->DisplaySize.y * draw_data->FramebufferScale.y);
     glViewport(0, 0, width, height);
 
-	glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
+	glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
 	glClear(GL_COLOR_BUFFER_BIT);
 	ImGui_ImplOpenGL2_RenderDrawData(draw_data);