Update README with missing parameters

Author: chrisbarr

README.md

@@ -56,7 +56,7 @@ Available methods:
 * `listSubscriptions()`
 * `listSubscriptionsByTopic($topicArn)`
 * `listTopics()`
-* `publish($topicArn, $message)`
+* `publish($topicArn, $message, $subject, $messageStructure)`
 * `removePermission($topicArn, $label)`
 * `setTopicAttributes($topicArn, $attrName, $attrValue)`
 * `subscribe($topicArn, $protocol, $endpoint)`

lib/AmazonSNS.php

@@ -306,7 +306,7 @@ public function listTopics($nextToken = null) {
 	 *
 	 * @link http://docs.amazonwebservices.com/sns/latest/api/API_Publish.html
 	 * @param string $topicArn
-	 * @param string $message 
+	 * @param string $message
 	 * @param string $subject [optional] Used when sending emails
 	 * @param string $messageStructure [optional] Used when you want to send a different message for each protocol.If you set MessageStructure to json, the value of the Message parameter must: be a syntactically valid JSON object; and contain at least a top-level JSON key of "default" with a value that is a string.
 	 * @return string