RapidJson 1.1 support + More move semantics

*Support for RapidJson 1.1, use TINYGLTF_USE_RAPIDJSON to toggle between RapidJson and nlohmann

*Lot more move semantics enabled.  All parsing and serialization now move all json objects with far fewer copies

loader_example.cc

@@ -4,6 +4,7 @@
 #define TINYGLTF_IMPLEMENTATION
 #define STB_IMAGE_IMPLEMENTATION
 #define STB_IMAGE_WRITE_IMPLEMENTATION
+//#define TINYGLTF_USE_RAPIDJSON
 #include "tiny_gltf.h"
 
 #include <cstdio>
@@ -742,5 +743,7 @@ int main(int argc, char **argv) {
 
   Dump(model);
 
+  gltf_ctx.WriteGltfSceneToFile(&model, "test.gltf");
+
   return 0;
 }