Add support for nxxm.

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

include/ftxui/util/autoreset.hpp

@@ -0,0 +1,22 @@
+#ifndef FTXUI_UTIL_AUTORESET_HPP
+#define FTXUI_UTIL_AUTORESET_HPP
+
+namespace ftxui {
+
+template<typename T>
+class AutoReset {
+ public:
+  AutoReset(T* variable, T new_value)
+      : variable_(variable),
+        previous_value_(std::move(*variable)) {
+    *variable_ = std::move(new_value);
+  }
+  ~AutoReset() { *variable_ = std::move(previous_value_); }
+ private:
+  T* variable_;
+  T previous_value_;
+};
+
+} // namespace ftxui
+
+#endif /* end of include guard: FTXUI_UTIL_AUTORESET_HPP */