When we are retrieving the value, and the SignedSerializer fails because
of invalid signature for example we want to simply return None, as if
there was no cookie set in the first place.

  to ``\\`` when quoting cookie values.  Now, instead, cookie serialization
  generates ``\042`` for the doublequote and ``\134`` for the backslash. This
  is what is expected as per RFC 6265.  Note that old cookie values that do
  have the older style quoting in them will still be unquoted correctly,
  however.

  did not need to be quoted per RFC 6265.  The following characters are no
  longer quoted in cookie values: ``~/=<>()[]{}?@`` .  The full set of
  non-letter-or-digit unquoted cookie value characters is now
  ``!#$%&'*+-.^_`|~/: =<>()[]{}?@``.  See
  http://tools.ietf.org/html/rfc6265#section-4.1.1 for more information.

- Cookie names are now restricted to the set of characters expected by RFC
  6265.  Previously they could contain unsupported characters such as ``/``.

- 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.

Do note that currently tests seem to fail under Python 3.2 and Python
3.3.