Bpipe 980 (TwilioDevEd#777)

* BPIPE-980: Help file updates for as_of field to usage APIs

* as_of date in response

Author: vchoudhari45

rest/usage-records/list-get-example-1/output/list-get-example-1.json

@@ -26,7 +26,8 @@
          "price_unit": "usd", 
          "subresource_uris": null, 
          "description": "Inbound ShortCode SMS", 
-         "end_date": "2012-09-30", 
+         "end_date": "2012-09-30",
+         "as_of": "2012-09-30T21:59:05+00:00",
          "usage_unit": "messages", 
          "price": "0", 
          "uri": "/2010-04-01/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Usage/Records/LastMonth.json?Category=sms-inbound-shortcode&StartDate=2012-09-01&EndDate=2012-09-30",