'Return all instance resources using an iterator
This will fetch a page of resources from the API and yield them in
turn. When the page is exhausted, this will make a request to the API
to retrieve the next page. Hence you may notice a pattern - the library
will loop through 50 objects very quickly, but there will be a delay
retrieving the 51st as the library must make another request to the API
for resources.
Example usage:
.. code-block:: python
for message in client.messages:
print message.sid'

def iter(self, **kwargs):

    params = transform_params(kwargs)
    while True:
        (resp, page) = self.request('GET', self.uri, params=params)
        if (self.key not in page):
            raise StopIteration()
        for ir in page[self.key]:
            (yield self.load_instance(ir))
        if (not page.get('next_page_uri', '')):
            raise StopIteration()
        o = urlparse(page['next_page_uri'])
        params.update(parse_qs(o.query))
