added the ability to make a model `keyless`
added the ability to define the type directly as the value of the key (as a string)
added a test for keyless models
added the ability to define another model as a property
added a `__model` property for type checking
refactored the attributes to make them a little more robust
added a test to check when a model was defined as the direct value of a property
build dist
0.0.9