Add CoolSMS PHP SDK, and update Composer dependencies

vendor/coolsms/php-sdk/examples/GroupMessage/example_send_process.php

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+<?php
+/**
+ * #example_send_process
+ *
+ * This sample code demonstrate how to send group message through CoolSMS Rest API PHP
+ * for more info, visit
+ * www.coolsms.co.kr
+ */
+
+use Nurigo\Api\GroupMessage;
+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 {
+	$options = new stdClass();
+
+    // initiate rest api sdk object
+	$rest = new GroupMessage($api_key, $api_secret);
+
+    // create group
+	$result = $rest->createGroup($options);
+	$group_id = $result->group_id;
+	print_r($result);
+
+	// add messages
+	$options->to = '01000000000';
+    $options->from = '01000000000';
+    $options->text = '안녕하세요. 10000건을 20초안에 발송하는 빠르고 저렴한 CoolSMS의 테스팅 문자입니다. ';
+	$options->group_id = $group_id;	// group id
+	$result = $rest->addMessages($options);
+	print_r($result);
+
+	// send messages
+	$result = $rest->sendGroupMessage($group_id);
+    print_r($result);
+} catch(CoolsmsException $e) {
+    echo $e->getMessage(); // get error message
+    echo $e->getCode(); // get error code
+}