Rewrite and revert some code to build in pre-C++11

Rewerite and revert some code that this library can be built in pre-C++11 and C++11 env.
Main Change List:
1. using -> typedef
2. not using auto & decltype
3. not using raw string literals
4. ..., other c++11 features will be chosen to compile, depending on env.

example/readFromString/readFromString.cpp

@@ -1,4 +1,5 @@
 #include "json/json.h"
+#include <cstdlib>
 #include <iostream>
 /**
  * \brief Parse a raw string into Value object using the CharReaderBuilder
@@ -10,9 +11,9 @@
  * 20
  */
 int main() {
-  const std::string rawJson = R"({"Age": 20, "Name": "colin"})";
-  const auto rawJsonLength = static_cast<int>(rawJson.length());
-  constexpr bool shouldUseOldWay = false;
+  const std::string rawJson = "{\"Age\": 20, \"Name\": \"colin\"}";
+  const int rawJsonLength = static_cast<int>(rawJson.length());
+  JSONCPP_CONST bool shouldUseOldWay = false;
   JSONCPP_STRING err;
   Json::Value root;
 
@@ -21,12 +22,13 @@ int main() {
     reader.parse(rawJson, root);
   } else {
     Json::CharReaderBuilder builder;
-    const std::unique_ptr<Json::CharReader> reader(builder.newCharReader());
+    Json::CharReader* reader(builder.newCharReader());
     if (!reader->parse(rawJson.c_str(), rawJson.c_str() + rawJsonLength, &root,
                        &err)) {
       std::cout << "error" << std::endl;
       return EXIT_FAILURE;
     }
+    delete reader;
   }
   const std::string name = root["Name"].asString();
   const int age = root["Age"].asInt();