Add SMS support

Summary:
Provides a working SMS implementation with support for Twilio.

This version doesn't really retry if we get any gruff at all. Future versions should retry.

Test Plan: used bin/sms to send messages and look at them.

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: aurelijus, epriestley, Korvin

Maniphest Tasks: T920

Differential Revision: https://secure.phabricator.com/D8930

externals/twilio-php/Services/Twilio/Rest/CredentialListMapping.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * A single CredentialListMapping
+ *
+ * .. php:attr:: date_created
+ *
+ *    The date this mapping was created
+ *
+ * .. php:attr:: date_updated
+ *
+ *    The date this mapping was updated
+ *
+ * .. php:attr:: sid
+ *
+ *    The sid of this mapping
+ *
+ * .. php:attr:: friendly_name
+ *
+ *    The friendly name of this mapping
+ *
+ * .. php:attr:: uri
+ *
+ *    The uri of this mapping
+ *
+ * .. php:attr:: subresource_uris
+ *
+ *    The subresources associated with this mapping (Credentials)
+ */
+
+class Services_Twilio_Rest_CredentialListMapping extends Services_Twilio_InstanceResource {
+    protected function init($client, $uri) {
+        $this->setupSubresources(
+            'credentials'
+        );
+    }
+}