Haravan

* Removed support for legacy auth
* Updated to pyactiveresource v2.0.0 which changes the default form to JSON
* in Session::request_token params is no longer optional, you must pass all the params
and the method will now extract the code
* made create_permission_url an instance method, you'll need an instance
of session to call this method from now on
* Updated session.request_token
* Updated Session to better match the HaravanAPI Ruby gem
* Updated the readme to better describe how to use the library
* Added support for CustomerSavedSearch (CustomerGroup is deprecated)

* Fix thread local headers to store a copy of the default hash which
prevents activate_session in one thread from affecting other threads.

* Fix deserializing and serializing fulfillments which can now contain
arrays of strings in the tracking_urls attribute.

* Fix parameter passing for order cancellation.
* Fix Product.price_range method for variants with different prices.

* Fixed another bug in Image size methods regex.

* Fix bug in setting format attribute on Webhook instances.
* Fixed missing slash in return value of Image size methods
* Upgrade pyactiveresource to fix unicode encoding issues