Add clang-tidy. (#368)

.clang-tidy

CMakeLists.txt

cmake/ftxui_set_options.cmake

examples/CMakeLists.txt

examples/component/checkbox_in_frame.cpp

examples/component/menu_entries.cpp

examples/component/menu_style.cpp

examples/dom/border.cpp

examples/dom/color_gallery.cpp

examples/dom/graph.cpp

examples/dom/window.cpp

examples/index.html

include/ftxui/component/component.hpp

include/ftxui/component/component_options.hpp

include/ftxui/component/event.hpp

include/ftxui/dom/canvas.hpp

include/ftxui/dom/deprecated.hpp

include/ftxui/dom/elements.hpp

include/ftxui/dom/flexbox_config.hpp

include/ftxui/dom/node.hpp