Add support for nxxm.

CMakeLists.txt

README.md

examples/CMakeLists.txt

examples/html/test.html

examples/util/CMakeLists.txt

examples/util/print_key_press.cpp

ftxui/CMakeLists.txt

include/ftxui/README.md

include/ftxui/component/checkbox.hpp

include/ftxui/component/component.hpp

include/ftxui/component/container.hpp

include/ftxui/component/event.hpp

include/ftxui/component/input.hpp

include/ftxui/component/menu.hpp

include/ftxui/component/radiobox.hpp

include/ftxui/component/screen_interactive.hpp

include/ftxui/component/toggle.hpp

include/ftxui/dom/elements.hpp

include/ftxui/dom/node.hpp

include/ftxui/dom/requirement.hpp