v0.13.0

* Update `test/support` folders structure (#49)
* Add stacks to MR, allow creating full stacks of models (#50)
* Setup `FakeRecord` to work with MR stacks (#51)
* Update factory and stack file's structure (#52)
* Integrate stacks with factories (#53)
* Allow passing nested fields/attributes to factories (#54)
* Factory speed improvements (#55)
* Fix empty test, ensure fields/associations can be supered to (#56)
* Track the model class on it's record class (#57)
* Make providing a class name optional for model associations (#58)
* Use better AR association methods for factories/stacks (#59)
* Commonize applying args logic in factories (#60)
* Have factories build associations when provided in defaults (#61)
* Have stacks take instances instead of classes (#62)
* Allow easily configuring model class for `FakeRecord` (#63)
* Make class name optional for fake record associations (#64)
* Setup model associations for polymorphic associations (#65)
* Add polymorphic model associations (#66)