Add the Button component.

src/ftxui/component/button.cpp

@@ -0,0 +1,26 @@
+#include "ftxui/component/button.hpp"
+
+#include <functional>
+
+namespace ftxui {
+
+Element Button::Render() {
+  if (Focused())
+    return text(label) | border |inverted;
+  else
+    return text(label) | border;
+}
+
+bool Button::OnEvent(Event event) {
+  if (event == Event::Return) {
+    on_click();
+    return true;
+  }
+  return false;
+}
+
+}  // namespace ftxui
+
+// 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.