Delete records from Exact Target

* Add a method to delete a subscriber's record from one of our Exact
  Target data extensions, given the token.
* Manually tested with my own data extensions, verified that it deletes
  the desired record and no others.
Bug 853990 Fix suds cache usage

We made a change to use our own cache with Suds, but it turns out that
Suds uses named type checking to validate the cache instead of duck
typing, so we need to inherit from Suds's cache even though we don't
use anything from it.
Merge pull request #77 from dpoirier/bug-853990-fix-suds-cache

Bug 853990 Fix suds cache usage
Merge pull request #76 from dpoirier/delete-et-record

Delete records from Exact Target
Bug 901541 - Newsletter recovery email

Add API that given an email address, sends an email to that address
with a link to allow that user to manage their subscriptions.