Refactor the surrogate keys we've used
Refactor AttributeDict

* Moves AttributeDict into warehouse.datastructures
* Refactors convert_to_attr_dict to just be the __init__ for
  AttributeDict
Declare constants for the Fastly surrogate keys
Add pretend and mock to dev dependencies
Merge pull request #266 from sharoonthomas/master

Add pretend and mock to dev dependencies
Merge pull request #265 from dstufft/refactor-fastly-cache

Use a Standard Set of Fastly Surrogate Keys
Merge pull request #271 from agronholm/master

Updated setup.py to indicate that it runs on Python 3.4+
Allow whitelisting the CDN for trusting the X-Forwarded-* headers
Merge pull request #272 from dstufft/x-forwarded

Allow whitelisting the CDN for trusting the X-Forwarded-* headers
Simplified the database setup in conftest.py and removed unnecessary explicit engine.connect() calls from the various db.py modules