Add RadioBox.

examples/component/radiobox.cpp

@@ -0,0 +1,19 @@
+#include "ftxui/component/radiobox.hpp"
+#include "ftxui/component/component.hpp"
+#include "ftxui/component/container.hpp"
+#include "ftxui/component/screen_interactive.hpp"
+
+using namespace ftxui;
+
+int main(int argc, const char* argv[]) {
+  auto screen = ScreenInteractive::TerminalOutput();
+  RadioBox radiobox;
+  radiobox.entries = {
+      L"Use gcc",
+      L"Use clang",
+      L"Use emscripten",
+      L"Use tcc",
+  };
+  screen.Loop(&radiobox);
+  return 0;
+}