Coverage decorator (#384)

.github/workflows/build.yaml

README.md

cmake/ftxui_test.cmake

include/ftxui/screen/terminal.hpp

src/ftxui/dom/blink_test.cpp

src/ftxui/dom/bold_test.cpp

src/ftxui/dom/border_test.cpp

src/ftxui/dom/color_test.cpp

src/ftxui/dom/dim_test.cpp

src/ftxui/dom/separator_test.cpp

src/ftxui/dom/underlined_test.cpp

src/ftxui/screen/color.cpp

src/ftxui/screen/color_test.cpp

src/ftxui/screen/terminal.cpp