factoryFor return value should be {create, class}

[mixonic]

factoryFor currently returns the factory literal. Ember's factoryFor returns an object {create, class}. class is simply the registered item. create is a function accepting an argument of initial properties for the instance, and returns an instance of the factory with dependencies injected. See the above links for implementation details.

@robbiepitts was attempting to use factoryFor on glimmer/di and noted the dependencies are missing. This probably means factoryFor on glimmer/di should be refactored to match Ember's behavior or that a new API is needed for glimmer/di.

[dgeb]

Implemented in #26

[dgeb]

Just merged #26