Add support for nxxm.

[nxxm](https://nxxm.github.io)

include/ftxui/component/input.hpp

@@ -0,0 +1,33 @@
+#ifndef FTXUI_COMPONENT_INPUT_H_
+#define FTXUI_COMPONENT_INPUT_H_
+
+#include "ftxui/component/component.hpp"
+#include <functional>
+
+namespace ftxui {
+
+class Input : public Component {
+ public:
+  // Constructor.
+  Input() = default;
+  ~Input() override = default;
+
+  // State.
+  std::wstring content;
+  std::wstring placeholder;
+
+  // State update callback.
+  std::function<void()> on_change = [](){};
+  std::function<void()> on_enter = [](){};
+
+  // Component implementation.
+  Element Render() override;
+  bool OnEvent(Event) override;
+
+ private:
+  int cursor_position = 0;
+};
+
+}  // namespace ftxui
+
+#endif /* end of include guard: FTXUI_COMPONENT_INPUT_H_ */