Extracted StringReader and StringWriter from JsonParser

Split `Internals/` folder into `Data/`, `Deserialization/`, `Serialization/`

include/ArduinoJson/Data/ListNode.hpp

@@ -0,0 +1,27 @@
+// Copyright Benoit Blanchon 2014-2016
+// MIT License
+//
+// Arduino JSON library
+// https://github.com/bblanchon/ArduinoJson
+// If you like this project, please add a star!
+
+#pragma once
+
+#include <stddef.h>  // for NULL
+
+#include "JsonBufferAllocated.hpp"
+
+namespace ArduinoJson {
+namespace Internals {
+
+// A node for a singly-linked list.
+// Used by List<T> and its iterators.
+template <typename T>
+struct ListNode : public Internals::JsonBufferAllocated {
+  ListNode() : next(NULL) {}
+
+  ListNode<T> *next;
+  T content;
+};
+}
+}