Add CoolSMS PHP SDK, and update Composer dependencies

vendor/coolsms/php-sdk/examples/Message/example_get_balance.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * #example_balance
+ *
+ * This sample code demonstrate how to check cash & point balance through CoolSMS Rest API PHP
+ * for more info, visit
+ * www.coolsms.co.kr
+ */
+
+use Nurigo\Api\Message;
+use Nurigo\Exceptions\CoolsmsException;
+
+require_once __DIR__ . "/../../bootstrap.php";
+
+
+// api_key and api_secret can be obtained from www.coolsms.co.kr/credentials
+$api_key = '#ENTER_YOUR_OWN#';
+$api_secret = '#ENTER_YOUR_OWN#';
+
+try {
+    // initiate rest api sdk object
+    $rest = new Message($api_key, $api_secret);
+
+    $result = $rest->getBalance();
+    print_r($result);
+} catch (CoolsmsException $e) {
+    echo $e->getMessage(); // get error message
+    echo $e->getCode(); // get error code
+}