Update docs/usage/queues.rst

/conferences/queues/
docs: usage: caller-ids: add a delete example

The Twilio-python docs are not clear on how to delete a callerID so I added an example
http://twilio-python.readthedocs.org/en/latest/api/rest/resources.html#caller-ids
fix some warnings when building the docs.
fix various typos
add newline at end of file
Add update() to the usage trigger list resource
Added Twilio error code to TwilioRestException
Set the Twilio error code in make_twilio_request