Using value from #4 as resultimg type, make safe expression evaluator.

Measure speed of expression evaluation.

Right now both type and value bit widths are represented by Peano encoded naturals. This is required for Types and associated singletons, but it would be nice if runtime value ie Demote Nat would be Natural. However Natural is already taken by singletons (library) Nat. That is why we need to create newtype wrapper over Natural.

This will allow us to write our own instance of SingKind with proper demoted associated type.

Come up with appropriate type for representing state. Since statements can modify that state interpreter should be something like: State RtlState.

We mostly care for final state, that will contain values for all outputs from Module.
Other important task for interpreter is to perform all side effects like prints.

RTL values can be Valid or Invalid. Any operation involving Invalid value yields another Invalid.

Valid values can are characterized by its type (Ty or RTy). It would be nice to have basic set of typeclasses instances for those like Num or Bounded.