Guard against there not being an active_card or subscription
2.0b23
Added a  field to CurrentSubscription and updated the  method to properly check the status, cancel_at_period_end, and current_period_end flags.
Make sending email receipts configurable
Fix whitespace issues
Fixed whitespace issues
Make stripe_id non-unique for an InvoiceItem
Delete CurrentSubscription when syncing with Stripe if it has been deleted in Stripe
Merge pull request #81 from OysterBooks/invoiceitem-stripeid-fix

Make stripe_id non-unique for an InvoiceItem
Merge branch 'master' of github.com:eldarion/django-stripe-payments
Merge branch 'sync-deleted-subscription-fix' of github.com:OysterBooks/django-stripe-payments into OysterBooks-sync-deleted-subscription-fix

Conflicts:
	payments/models.py
Merge branch 'configurable-email-receipts' of github.com:OysterBooks/django-stripe-payments into OysterBooks-configurable-email-receipts

Conflicts:
	payments/models.py
Merge branch 'custom-user-model-admin-fix' of github.com:OysterBooks/django-stripe-payments into OysterBooks-custom-user-model-admin-fix

Conflicts:
	payments/__init__.py
	payments/models.py
Merge branch 'subscription-cancellation-cleanup' of github.com:OysterBooks/django-stripe-payments into OysterBooks-subscription-cancellation-cleanup

Conflicts:
	payments/models.py
Clean up style
Fix bug where list wasn't getting extended
Pin pylint to 0.27.0
Merged upsteram master and fixed positional argument string formatting