Values tracking

In several cases using just types to create contracts is just not enough. The example is FactoryGirl's mock class [creation](http://www.rubydoc.info/gems/factory_girl/file/GETTING_STARTED.md#Using_factories) which returns objects of class derivable from symbol value by fixed algorithm, for example, underscore->camelcase conversion.

One could achieve such results by sending the values of some string/symbol type arguments along with their types. Unfortunately, doing so plainly must dramatically reduce the speed of arg-scanner execution (which is not great already).

The possible approach is to consider only the "short" values given as a separate parameter OR as an explicit hash value (required to deal with `factory :admin, class: User do` calls)