Move CharacterIterator family into corelib/text directory
Even though CharacterIterator interface and its implementation class(es) are members of ascension.text namespace, character-iterator.hpp is ascension/corelib.
We move this file into ascension/corelib/text directory.
Even though CharacterIterator interface and its implementation class(es) are members of ascension.text namespace, character-iterator.hpp is ascension/corelib.
We move this file into ascension/corelib/text directory.