Add MenuEntry. (#199)

This will address comments from:
https://github.com/ArthurSonzogni/FTXUI/issues/194

examples/component/CMakeLists.txt

@@ -11,6 +11,7 @@ example(input)
 example(menu)
 example(menu2)
 example(menu_multiple)
+example(menu_entries)
 example(menu_style)
 example(modal_dialog)
 example(print_key_press)

examples/component/menu_entries.cpp

@@ -0,0 +1,90 @@
+#include <functional>  // for function
+#include <iostream>  // for basic_ostream::operator<<, operator<<, endl, basic_ostream, basic_ostream<>::__ostream_type, cout, ostream
+#include <string>    // for string, basic_string, allocator
+#include <vector>    // for vector
+
+#include "ftxui/component/captured_mouse.hpp"      // for ftxui
+#include "ftxui/component/component.hpp"           // for Menu
+#include "ftxui/component/component_options.hpp"   // for MenuOption
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+using namespace ftxui;
+
+// Define a special style for some menu entry.
+MenuEntryOption Colored(ftxui::Color c) {
+  MenuEntryOption special_style;
+  special_style.style_normal = Decorator(color(c));
+  special_style.style_focused = Decorator(color(c)) | inverted;
+  special_style.style_selected = Decorator(color(c)) | bold;
+  special_style.style_selected_focused = Decorator(color(c)) | inverted | bold;
+  return special_style;
+}
+
+int main(int argc, const char* argv[]) {
+  auto screen = ScreenInteractive::TerminalOutput();
+
+    //Black        = 0,
+    //Red          = 1,
+    //Green        = 2,
+    //Yellow       = 3,
+    //Blue         = 4,
+    //Magenta      = 5,
+    //Cyan         = 6,
+    //GrayLight    = 7,
+    //GrayDark     = 8,
+    //RedLight     = 9,
+    //GreenLight   = 10,
+    //YellowLight  = 11,
+    //BlueLight    = 12,
+    //MagentaLight = 13,
+    //CyanLight    = 14,
+    //White        = 15,
+
+  int selected = 0;
+  auto menu = Container::Vertical(
+      {
+          MenuEntry(" 1. improve"),
+          MenuEntry(" 2. tolerant"),
+          MenuEntry(" 3. career"),
+          MenuEntry(" 4. cast"),
+          MenuEntry(" 5. question"),
+
+          Renderer([] { return separator(); }),
+
+          MenuEntry(" 6. rear", Colored(Color::Red)),
+          MenuEntry(" 7. drown", Colored(Color::Yellow)),
+          MenuEntry(" 8. nail", Colored(Color::Green)),
+          MenuEntry(" 9. quit", Colored(Color::Cyan)),
+          MenuEntry("10. decorative", Colored(Color::Blue)),
+
+          Renderer([] { return separator(); }),
+
+          MenuEntry("11. costume"),
+          MenuEntry("12. pick"),
+          MenuEntry("13. oral"),
+          MenuEntry("14. minister"),
+          MenuEntry("15. football"),
+          MenuEntry("16. welcome"),
+          MenuEntry("17. copper"),
+          MenuEntry("18. inhabitant"),
+          MenuEntry("19. fortune"),
+      },
+      &selected);
+
+  // Display together the menu with a border
+  auto renderer = Renderer(menu, [&] {
+    return vbox({
+               hbox(text("selected = "), text(std::to_string(selected))),
+               separator(),
+               menu->Render() | frame | size(HEIGHT, LESS_THAN, 10),
+           }) |
+           border;
+  });
+
+  screen.Loop(renderer);
+
+  std::cout << "Selected element = " << selected << std::endl;
+}
+
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.