Add support for nxxm.

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

include/ftxui/dom/take_any_args.hpp

@@ -0,0 +1,30 @@
+#include <type_traits>
+
+template <class T>
+void Merge(Elements& container, T t) {}
+
+template <>
+inline void Merge(Elements& container, Element element) {
+  container.push_back(std::move(element));
+}
+
+template <>
+inline void Merge(Elements& container, Elements elements) {
+  for(auto& element : elements)
+    container.push_back(std::move(element));
+}
+
+// Turn a set of arguments into a vector.
+template <class... Args>
+Elements unpack(Args... args) {
+  std::vector<Element> vec;
+  (Merge(vec, std::move(args)), ...);
+  return vec;
+}
+
+// Make |container| able to take any number of argments.
+#define TAKE_ANY_ARGS(container) \
+template <class... Args> \
+Element container(Args... children) { \
+  return container(unpack(std::forward<Args>(children)...)); \
+}