Terraformpy

Allow ResourceCollection to be used in ModelType fields

Ensure the TypedObjecAttr class, added in 1.0.1, works as StringType inputs in ResourceCollection

* Add support for map indices access: https://www.terraform.io/docs/configuration/expressions.html#indices-and-attributes

* **BREAKING** - The `Input()` primitive originally shipped with terraformpy is now fully deprecated.
All inputs must be defined as schematics types.

* `ResourceCollection` is now a specialized subclass of a schematics `Model`

* Support Schematics style field level validation (33)

* Add a changelog