Squashed commit of the following:
- minor refactoring of [IterableFactory] and completed test coverage for [Iterable_Integer_next], [Iterable_Integer_next_previous] and [Iterable_Integer_next_previous_StopIteration].
- minor refactoring of two of the "Iterable_Integer" test specifications.
- completed test coverage for [Iterable_Character_next], [Iterable_Character_next_previous] and [Iterable_Character_next_previous_StopIteration].