Basic GovUkDelivery client and methods

GovUkDelivery allows clients to subscribe new email addresses, create
lists (a synonym for a specific mailing list), and send notifications to
said lists.

Includes test helpers for use in this project and others.
Add :noop configuration method that does nothing

This is for development purposes. Additionally an @options argument of
:stdout will cause the API methods to print their payloads.
Trim down helpers and verify requests are made
Make sure the timeout is 10 seconds
Remove TODO I'm not going TO DO
Merge pull request #55 from alphagov/govuk-delivery

Basic GovUkDelivery client and methods