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1. Improved the code of :class:`mosql.result.Model`.
2. Added :meth:`mosql.result.Model.new`.
3. Added :meth:`mosql.result.Model.add`.
4. Added :meth:`mosql.result.Model.clear`.
5. The :meth:`mosql.result.Model.perform` now supports to call procedure,
execute SQL with parameter and `executemany`.
6. Fixed the compatibility with MySQL.