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/stringWrite/stringWrite.cpp

@@ -0,0 +1,33 @@
+#include "json/json.h"
+#include <iostream>
+/** \brief Write a Value object to a string.
+ * Example Usage:
+ * $g++ stringWrite.cpp -ljsoncpp -std=c++11 -o stringWrite
+ * $./stringWrite
+ * {
+ *     "action" : "run",
+ *     "data" :
+ *     {
+ *         "number" : 1
+ *     }
+ * }
+ */
+int main() {
+  Json::Value root;
+  Json::Value data;
+  constexpr bool shouldUseOldWay = false;
+  root["action"] = "run";
+  data["number"] = 1;
+  root["data"] = data;
+
+  if (shouldUseOldWay) {
+    Json::FastWriter writer;
+    const std::string json_file = writer.write(root);
+    std::cout << json_file << std::endl;
+  } else {
+    Json::StreamWriterBuilder builder;
+    const std::string json_file = Json::writeString(builder, root);
+    std::cout << json_file << std::endl;
+  }
+  return EXIT_SUCCESS;
+}