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/docs/usage/rest/sms-messages.rst

@@ -0,0 +1,50 @@
+=============
+SMS Messages
+=============
+
+Sending a SMS Message
+=====================
+
+
+The :php:class:`Services_Twilio_Rest_SmsMessages` resource allows you to send
+outgoing text messages.
+
+.. code-block:: php
+
+    require('/path/to/twilio-php/Services/Twilio.php');
+
+    $client = new Services_Twilio('AC123', '123');
+    $message = $client->account->sms_messages->create(
+      '+14085551234', // From a Twilio number in your account
+      '+12125551234', // Text any number
+      "Hello monkey!"
+    );
+
+    print $message->sid;
+
+Listing SMS Messages
+====================
+
+It's easy to iterate over your SMS messages.
+
+.. code-block:: php
+
+    $client = new Services_Twilio('AC123', '123');
+    foreach ($client->account->sms_messages as $message) {
+        echo "From: {$message->from}\nTo: {$message->to}\nBody: " . $message->body;
+    }
+
+Filtering SMS Messages
+======================
+
+Let's say you want to find all of the SMS messages that have been sent from
+a particular number. You can do so by constructing an iterator explicitly:
+
+.. code-block:: php
+
+    $client = new Services_Twilio('AC123', '123');
+    foreach ($client->account->sms_messages->getIterator(0, 50, array(
+        'From' => '+14105551234',
+    )) as $message) {
+        echo "From: {$message->from}\nTo: {$message->to}\nBody: " . $message->body;
+    }