Add strings_differ for SignedSerializer
Add SignedSerializer
Add CookieProfile class

This object can be used in conjunction with a Request object to parse
information from a cookie, or it can create new cookies that are
automatically set on a response or just passed back to the user.
Add SignedCookieProfile

Uses an secure HMAC to sign cookies before sending them to the web
browser, this way if it is tampered with it is easy to verify.
Add tests for all the new stuff

Do note that currently tests seem to fail under Python 3.2 and Python
3.3.
- Make tests pass on Python 3.

- Treat serializer as a single entity instead of having separate serialize
  and deserialize functions.

- Don't have a "_default_serializer" class attr as the only reason to do
  this would be if it were overrideable and it's not because it's
  underscored.

- 79 columns.

- Add changelog entry and update docs.
doc generation fixes