Flask-dance

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* Allowed an ``oauth_authorized`` event handler to return a ``flask.Response``
instance. If so, that response will be sent to the requesting user.

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* Fixed an error that occurred if you were running an unreleased version
of Flask, due to the version comparison code. See `issue 53`_.
Thanks, ThiefMaster!

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* If the OAuth 1 token request is denied on accessing the login view,
Flask-Dance will now redirect the user and fire the ``oauth_error`` signal.
This matches the behavior of how Flask-Dance handles OAuth 2 errors.

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* Fixed a typo in the Slack configuration, where it would load the OAuth 2
client secret from a config variable named "SLLACK_OAUTH_CLIENT_SECRET"
instead of "SLACK_OAUTH_CLIENT_SECRET"

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* Added the Slack pre-set configuration
* Fixed a subtle bug where setting the ``client_id`` property on an instance
of ``OAuth2ConsumerBlueprint`` did not update the value that the ``oauthlib``
library uses to create the redirect URL in the login step. ``client_id`` is
now a dynamic property on ``OAuth2ConsumerBlueprint``, which sets the
``client_id`` property on the wrapped ``oauthlib`` client automatically.
* Added some debug log statements to ``OAuth2ConsumerBlueprint``
* You can now define a ``session_created`` method on subclasses of
``OAuth2ConsumerBlueprint``. If you do, it will be called when a Requests
session is dynamically created, so that the session can be modified before
it is returned.

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* Removed the Dictective utility class, and replaced it with
``werkzeug.datastructures.CallbackDict``. It does the same thing, but
it's better tested, and already a part of one of Flask-Dance's dependencies.
* If the user hits the ``authorized`` view without having a "state" variable
set in the browser cookies, Flask-Dance will now redirect the user back
to the ``login`` view to start the OAuth dance all over again, rather than
raising a ``KeyError``.