add sender to the param list for the send/message API method

api/controllers/send_api_controller.rb

@@ -10,7 +10,8 @@ controller :send do
     param :to, "The e-mail addresses of the recipients (max 50)", :type => Array
     param :cc, "The e-mail addresses of any CC contacts (max 50)", :type => Array
     param :bcc, "The e-mail addresses of any BCC contacts (max 50)", :type => Array
-    param :from, "The e-mail address of the sender", :type => String
+    param :from, "The e-mail address for the From header", :type => String
+    param :sender, "The e-mail address for the Sender header", :type => String
     param :subject, "The subject of the e-mail", :type => String
     param :tag, "The tag of the e-mail", :type => String
     param :reply_to, "Set the reply-to address for the mail", :type => String