Implement a lot of new features.

This commit deserve to be cut into at least 8 sub commit. Sorry, I
acknowledge this is bad... Here are the new features:

 * dom decorator: bold, dim, underlined, inverted.
 * component mechanism
 * components
   * menu
   * toogle

examples/print_key_press/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_executable(print_key_press
+  main.cpp
+)
+target_link_libraries(print_key_press PRIVATE ftxui)