Improve the documentation.

doc/Doxyfile.in

doc/example_list.h

examples/dom/color_gallery.cpp

examples/dom/html_like.cpp

examples/dom/style_color.cpp

include/ftxui/component/component.hpp

include/ftxui/component/component_options.hpp

include/ftxui/dom/elements.hpp

include/ftxui/dom/take_any_args.hpp

src/ftxui/component/button.cpp

src/ftxui/component/catch_event.cpp

src/ftxui/component/checkbox.cpp

src/ftxui/component/component.cpp

src/ftxui/component/container.cpp

src/ftxui/component/input.cpp

src/ftxui/component/menu.cpp

src/ftxui/component/radiobox.cpp

src/ftxui/component/renderer.cpp

src/ftxui/component/toggle.cpp

src/ftxui/dom/composite_decorator.cpp