v0.5.1 - Minor features and some bug fixes

New features:

• exception_class_whitelist configuration option now applies to descendant exceptions
• Params other than id no longer raise and exception when deleting a resource
• When a resource is backed from an ArctiveRecord model the class name is read from the model by default

Bug fixes:

• Primary key (other than id) behavior has now been fixed.
• Error attributes and relationships are now using the formatter.
• Transactions are now used no matter how many operations are being processed
• All operations were being treated as transactional.