记录一种可读性较强好维护的字符串换行写法

 NSString *createTableSQL = @"CREATE TABLE GROUPTABLEV2 (id integer PRIMARY KEY autoincrement, "
                                   @"groupId text,name text, portraitUri text,inNumber text,maxNumber "
                                   @"text ,introduce text ,creatorId text,creatorTime text, isJoin "
                                   @"text, isDismiss text)";