增加查询信息的辅助函数
增加获取表和字段信息的方法
insert value of Expr convert to first_param
add table.iter() for Error "Socket receive buffer full"
change Row._data to object property
add Daily.migrate()
fix: Monthly.get_month_diff()
optimize methods of Table
change the second param of Table.save()
change Table.replace() to save()
Add subclass named Monthly