Add support for nxxm.

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

src/ftxui/component/event.cpp

@@ -0,0 +1,39 @@
+#include "ftxui/component/event.hpp"
+
+namespace ftxui {
+
+constexpr int ESC = int(27);
+
+// --- Character ---
+Event Event::Character(int c) {
+  return Event{c};
+}
+
+// --- Arrow ---
+Event Event::ArrowLeft{ESC, '[', 'D'};
+Event Event::ArrowRight{ESC, '[', 'C'};
+Event Event::ArrowUp{ESC, '[', 'A'};
+Event Event::ArrowDown{ESC, '[', 'B'};
+
+// --- Other ---
+Event Event::Backspace{127};
+Event Event::Delete{ESC, '[', '3', '~'};
+Event Event::Escape{ESC};
+Event Event::Return{10};
+
+Event Event::F1{ESC, '[', 'O', 'P'};
+Event Event::F2{ESC, '[', 'O', 'Q'};
+Event Event::F3{ESC, '[', 'O', 'R'};
+Event Event::F4{ESC, '[', 'O', 'S'};
+Event Event::F5{ESC, '[', '1', '5', '~'};
+Event Event::F6{ESC, '[', '1', '7', '~'};
+Event Event::F7{ESC, '[', '1', '8', '~'};
+Event Event::F8{ESC, '[', '1', '9', '~'};
+Event Event::F9{ESC, '[', '2', '0', '~'};
+Event Event::F10{ESC, '[', '2', '1', '~'};
+Event Event::F11{ESC, '[', '2', '1', '~'};  // Same as F10 ?
+Event Event::F12{ESC, '[', '2', '4', '~'};
+
+Event Event::Custom{0, 0, 0, 0, 0};
+
+} // namespace ftxui