Create an example directory and add some code examples. (#944)

* update example directory

* modify some compile error.

* update with clang-format

* update

* update

* add_definitions("../include/json")

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
#
# Date:      Wed Jul 10 21:26:16 2019 +0800
#
# On branch code_example
# Your branch is up-to-date with 'origin/code_example'.
#
# Changes to be committed:
#	modified:   example/CMakeLists.txt
#

* change CMakeLists.txt

* update streamWrite.cpp

* update

* Update readFromStream.cpp

* fix typo

example/readFromString/readFromString.cpp

@@ -0,0 +1,37 @@
+#include "json/json.h"
+#include <iostream>
+/**
+ * \brief Parse a raw string into Value object using the CharReaderBuilder
+ * class, or the legacy Reader class. 
+ * Example Usage: 
+ * $g++ readFromString.cpp -ljsoncpp -std=c++11 -o readFromString
+ * $./readFromString
+ * colin
+ * 20
+ */
+int main() {
+  const std::string rawJson = R"({"Age": 20, "Name": "colin"})";
+  const int rawJsonLength = static_cast<int>(rawJson.length());
+  constexpr bool shouldUseOldWay = false;
+  JSONCPP_STRING err;
+  Json::Value root;
+
+  if (shouldUseOldWay) {
+    Json::Reader reader;
+    reader.parse(rawJson, root);
+  } else {
+    Json::CharReaderBuilder builder;
+    const std::unique_ptr<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;
+    }
+  }
+  const std::string name = root["Name"].asString();
+  const int age = root["Age"].asInt();
+
+  std::cout << name << std::endl;
+  std::cout << age << std::endl;
+  return EXIT_SUCCESS;
+}