Add tests for requests_with_backoff
Implementing requests_with_backoff
Write should use backoffs
write does use backoffs!
Make pingdom collector use requests_with_backoff
docstring for _request_and_assert, response generator inside

Rob requested more clarity for the generic assertion code
Also, the generator is only used in _request_and_assert
Provide full requests API and stop importing as requests

As per Paul's suggestions:
* In requests_with_backoff we use 'from requests import *' so that we provide the full API of requests
* We no longer import as requests - instead we just use it as requests_with_backoff
Don't search directories we don't control with ack
Add venv, build and out to gitignore
Something like this to inject into the google client

only some responses throw errors, 502, 503 and 403 seem to be just
status codes on the response that we can read
any reading of status codes and throwing errors then must be already
handled by gapy or the google api client