JSONSerializer doesn't correctly handle CR characters

The JSON standard (see JSON.org) defines specific escape sequences for the following characters: \b, \f, \n, \r, \t and \uxxxx for other control characters. But the encoding logic in JSONSerializer doesn't match this list (particularly missing \r and not encoding other control characters using \uxxxx). The "writeObject" method only recognizes \t and \n and does not encode any control character less than 0xFF. The "readString" method seems a bit weird also in its handling of control characters in the input.