Add support for nxxm.

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

examples/util/CMakeLists.txt

@@ -0,0 +1,6 @@
+function(example name)
+  add_executable(${name} ${name}.cpp)
+  target_link_libraries(${name} PUBLIC component)
+endfunction(example)
+
+example(print_key_press)

examples/util/print_key_press.cpp

@@ -0,0 +1,48 @@
+#include <chrono>
+#include <iostream>
+#include <thread>
+
+#include "ftxui/component/component.hpp"
+#include "ftxui/component/screen_interactive.hpp"
+#include "ftxui/screen/string.hpp"
+
+using namespace ftxui;
+
+class DrawKey : public Component {
+ public:
+  ~DrawKey() override = default;
+
+  Element Render() override {
+    Elements children;
+    for (size_t i = std::max(0, (int)keys.size() - 10); i < keys.size(); ++i) {
+      std::string code = "";
+      for (size_t j = 0; j < 5; ++j)
+        code += " " + std::to_string(keys[i].values[j]);
+
+      try {
+        std::string line = code + " -> " + std::to_string(keys[i].values[0]) +
+                           " (" + char(keys[i].values[0]) + ")";
+        children.push_back(text(to_wstring(line)));
+      } catch (...) {
+        std::string line =
+            code + " -> " + std::to_string(keys[i].values[0]) + " (undefined)";
+        children.push_back(text(to_wstring(line)));
+      }
+    }
+    return vbox(std::move(children));
+  }
+
+  bool OnEvent(Event event) override {
+    keys.push_back(event);
+    return true;
+  }
+
+ private:
+  std::vector<Event> keys;
+};
+
+int main(int argc, const char* argv[]) {
+  auto screen = ScreenInteractive::FixedSize(80, 10);
+  DrawKey draw_key;
+  screen.Loop(&draw_key);
+}