Refactored function names of Question class to be PSR compliant. Related files have been adjusted accordingly.
Reformatted source and added missing function visibility.
Refactored get_level function name.
Updated the learnSet function to use a PDO transaction.
Reformatted source code and refactored get_random_weighted_kanjis to use PDO.
Adjusted some function names and corrected DB class output when error occurs.
Refactored get_random_kanjis to use PDO.