adding polymorphic_key arg to base column
adding polymorphic config to model metaclass
adding tests around polymorphic models
moving instance construction onto the model
moving polymorphic base discovery into model meta class
adding support for polymorphic model deserialization
adding tests around unindexed polymorphic columns
finishing up the unindexed polymorphic key tests
switching select query to all columns when defer and only fields aren't defined
adding support for auto filtering on polymorphic subclass models with and indexed polymorphic key
adding restriction around defining counter or container columns as polymorphic keys
adding custom validation
reverting custom validation changes
adding docs for polymorphic models and user defined validation
Merge branch 'master' into -1.8
fixing typo in docs