version to 0.19.0

* Added a benchmarking script (#94)
* Added mixin for read model query interface (#97)
* Added mixin for common read model "data" handling (#100)
* Added mixin for read model fields interface (#101)
* Expanded read model query interface (#103)
* Update read model mixin to use new behavior (#104)
* Added read model factory (#106)
* Allow primary key as read model column type (#108)
* Alias models as results for fake queries (#109)
* Instance exec read model query expression blocks (#110)
* Allow initializing a read model with no arguments (#111)
* Update to the latest NsOptions (ccf687cb4d)

**Note** This is version is not backwards compatible. Read models
have changed significantly and do not work as they previously did.

/cc @kellyredding