Adds unit tests for System.Char type checks.
Adds more tests and finishes the implementation of the IsTheSameButWithDifferentCaseAs() method (for char).
Adds more check methods to the char type:  IsALetter,  IsSameLetter, and renames the former: IsTheSameButWithDifferentCaseAs to the new: IsSameLetterButWithDifferentCaseAs

Now, the ToStringProperlyFormated() method also handle chars.