cpp/iterator/contiguous iterator

The concept refines  by providing a guarantee the denoted elements are stored contiguously in the memory.

Semantic requirements
Let and  be dereferenceable iterators and  be a non-dereferenceable iterator of type  such that  is reachable from  and  is reachable from. The type models  only if all the concepts it subsumes are modeled and:
 * , and
 * , and