Shopifyapi

- 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

- Made ShopifyResource.clear_session idempotent.

- Use the correct redirect parameter in Session.create_permission_url.
Was redirect_url but corrected to redirect_uri.

- Added support for OAuth2.
- ShopifyResource.activate_session must now be used with OAuth2 instead
of setting ShopifyResource.site directly.
- Session.**init** no longer allows params to be passed in as \*\*params
- Session.**init** now makes an HTTP request when using OAuth2 if
params are specified
- Session now exposes the access token through the token instance
variable to simplify session saving and resuming

- Using setup.py no longer requires all dependencies
- More compatibility fixes for using the latest pyactiveresource
- ShopifyResource.activate_session is not recommended over setting site
directly for forward compatibility with coming OAuth2 changes.

- Compatibility fixes for using latest (unreleased) pyactiveresource