Added RawJson() to insert pregenerated JSON portions (issue #259)

include/ArduinoJson/RawJson.hpp

@@ -0,0 +1,21 @@
+// 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
+
+namespace ArduinoJson {
+
+// A special type of data that can be used to insert pregenerated JSON portions.
+class RawJson {
+ public:
+  explicit RawJson(const char* str) : _str(str) {}
+  operator const char*() const { return _str; }
+
+ private:
+  const char* _str;
+};
+}