instance-based events #7

It would be useful if subscribers could receive events only related to a specific instance.

Scenario:

A web application lets users create their own AddressBook. Each AddressBook have many Contacts:

class AddressBook(models.Model):
    user = models.ForeignKey('auth.User')

@webhook_model(
    on_create=ModelEvent('contact.created'),
)
class Contact(models.Model):
    name = models.CharField(max_length=255)
    address_book = models.ForeignKey(AddressBook, related_name='contacts')

There doesn't seem to be a way for a subscriber to receive contact.created events only for Contacts of a specific AddressBook.