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

ftxui/include/ftxui/component/Event.hpp

@@ -0,0 +1,34 @@
+#ifndef FTXUI_COMPONENT_EVENT
+#define FTXUI_COMPONENT_EVENT
+
+namespace ftxui {
+namespace component {
+
+struct Event{
+  // --- Character ---
+  static Event Character(char);
+
+  // --- Arrow ---
+  static Event Arrow_Left;
+  static Event Arrow_Right;
+  static Event Arrow_Up;
+  static Event Arrow_Down;
+  
+  // --- Other ---
+  static Event Backspace;
+  static Event Delete;
+  static Event Escape;
+  static Event F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12;
+
+  // Internal representation.
+  int values [3];
+  Event(int values[3]) : values(values);
+
+};
+
+
+} // namespace component
+} // namespace ftxui
+
+
+#endif /* end of include guard: FTXUI_COMPONENT_EVENT */

ftxui/include/ftxui/component/component.hpp

@@ -0,0 +1,44 @@
+#ifndef FTXUI_COMPONENT_COMPONENT_HPP
+#define FTXUI_COMPONENT_COMPONENT_HPP
+
+#include "ftxui/dom/elements.hpp"
+#include "ftxui/component/delegate.hpp"
+
+namespace ftxui {
+namespace component {
+
+class Delegate;
+class Focus;
+
+class Component {
+ public:
+  // Constructor/Destructor.
+  Component(Delegate* delegate);
+  virtual ~Component();
+
+  // Render the component.
+  virtual dom::Element Render();
+
+  // Handle an event. By default, it calls this function on each children.
+  virtual bool Event(int key);
+
+  // If this component contains children, this indicates which one is active. It
+  // can be none of them.
+  // We say an element has the focus if the chain of GetActiveChild() from the
+  // root component contains this object.
+  virtual Component* GetActiveChild() { return nullptr; }
+  bool Active(); // True is this component is an active child.
+  bool Focused(); // True if all the ancestors are active childs.
+
+  Component* Parent();
+  Component* PreviousSibling();
+  Component* NextSibling();
+  
+ private:
+  Delegate* delegate_;
+};
+
+}  // namespace component
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_HPP */

ftxui/include/ftxui/component/component_direction.hpp

@@ -0,0 +1,25 @@
+#ifndef FTXUI_COMPONENT_COMPONENT_DIRECTION_H_
+#define FTXUI_COMPONENT_COMPONENT_DIRECTION_H_
+
+#include "ftxui/component/component.hpp"
+
+namespace ftxui {
+namespace component {
+
+// A component where focus and events are automatically handled for you.
+class ComponentDirection : public Component {
+ public:
+  ComponentDirection(Delegate* delegate);
+  bool Event(int key) override;
+  Component* GetActiveChild() override;
+
+ protected:
+  void Focus(Component* child);
+  virtual bool HandleDirection(int key) = 0;
+  Component* active_child_;
+};
+
+} // namespace component
+} // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_DIRECTION_H_ */

ftxui/include/ftxui/component/component_horizontal.hpp

@@ -0,0 +1,20 @@
+#ifndef FTXUI_COMPONENT_COMPONENT_HORIZONTAL_H_
+#define FTXUI_COMPONENT_COMPONENT_HORIZONTAL_H_
+
+#include "ftxui/component/component_direction.hpp"
+
+namespace ftxui {
+namespace component {
+
+// A component where focus and events are automatically handled for you.
+// It assumes its children are put in the horizontal direction.
+class ComponentHorizontal : public ComponentDirection {
+ public:
+  ComponentHorizontal(Delegate* delegate);
+  bool HandleDirection(int key) override;
+};
+
+} // namespace component
+} // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_HORIZONTAL_H_ */

ftxui/include/ftxui/component/component_vertical.hpp

@@ -0,0 +1,20 @@
+#ifndef FTXUI_COMPONENT_COMPONENT_VERTICAL_H_
+#define FTXUI_COMPONENT_COMPONENT_VERTICAL_H_
+
+#include "ftxui/component/component_direction.hpp"
+
+namespace ftxui {
+namespace component {
+
+// A component where focus and events are automatically handled for you.
+// It assumes its children are put in the vertical direction.
+class ComponentVertical : public ComponentDirection {
+ public:
+  ComponentVertical(Delegate* delegate);
+  bool HandleDirection(int key) override;
+};
+
+} // namespace component
+} // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_VERTICAL_H_ */

ftxui/include/ftxui/component/delegate.hpp

@@ -0,0 +1,34 @@
+#ifndef FTXUI_COMPONENT_DELEGATE_HPP
+#define FTXUI_COMPONENT_DELEGATE_HPP
+
+#include "ftxui/dom/elements.hpp"
+
+namespace ftxui {
+namespace component {
+
+class Component;
+
+class Delegate {
+ public:
+  Delegate() {}
+  virtual ~Delegate() {}
+
+  // A Delegate shadows a component.
+  virtual void Register(Component* component) = 0;
+  virtual Component* component() = 0;
+
+  // Create new children.
+  virtual Delegate* NewChild() = 0;
+  virtual std::vector<Delegate*> children() = 0;
+
+  // Navigate in the tree.
+  virtual Delegate* PreviousSibling() = 0;
+  virtual Delegate* NextSibling() = 0;
+  virtual Delegate* Parent() = 0;
+  virtual Delegate* Root() = 0;
+};
+
+}  // namespace component
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_DELEGATE_HPP */

ftxui/include/ftxui/component/menu.hpp

@@ -0,0 +1,31 @@
+#ifndef FTXUI_COMPONENT_MENU
+#define FTXUI_COMPONENT_MENU
+
+#include "ftxui/component/component.hpp"
+#include <functional>
+
+namespace ftxui {
+namespace component {
+
+class Menu : public Component {
+ public:
+  // Constructor.
+  Menu(Delegate*);
+
+  // State.
+  std::vector<std::wstring> entries = {};
+  int selected = 0;
+
+  // State update callback.
+  std::function<void()> on_change = [](){};
+  std::function<void()> on_enter = [](){};
+
+  // Component implementation.
+  dom::Element Render() override;
+	bool Event(int key) override;
+};
+
+}  // namespace component
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_MENU */

ftxui/include/ftxui/component/toggle.hpp

@@ -0,0 +1,31 @@
+#ifndef FTXUI_COMPONENT_TOGGLE_H_
+#define FTXUI_COMPONENT_TOGGLE_H_
+
+#include "ftxui/component/component.hpp"
+#include <functional>
+
+namespace ftxui {
+namespace component {
+
+class Toggle : public Component {
+ public:
+  // Constructor.
+  Toggle(Delegate*);
+
+  // State.
+  bool activated = true;
+  std::wstring on = L"On";
+  std::wstring off = L"Off";
+
+  // Callback.
+  std::function<void()> on_change = [](){};
+
+  // Component implementation.
+  dom::Element Render() override;
+	bool Event(int key) override;
+};
+
+}  // namespace component
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_TOGGLE_H_ */