Shopifyapi

- 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

- Added support for customer search and customer group search.
- Resource errors are cleared on save from previous save attempt.
- Made the library thread-safe using thread-local connections.

- Fixed a regression that caused a different connection
object to be created on each resource.

- Made responses available through the connection object.

- Added ability to add metafields on customers.