Use more strong rspec config
Move parameterized mixin to correct namespace

Rationale:

* A nullary parameterized evaluator is a nullary evaluator
* Arity only counts number of NODE children.
* The Nullary::Parameterized mixin now also applies only the needed
  Nullary inclusions.
* There are no method overrides within the same hierarchy anymore.
* Nullary parameterized evaluators do not need to include the Nullary
  mixin anymore
* Fixes all possible "order of inclusion" problems.