Support keyword argument to initially autocommit=on

[methane]

To avoid sending 2 unnecessary commands to MySQL when using autocommit mode.

[farcepest]

OK, I support doing this. However, there is a change I'd like to see:

autocommit = True: enables autocommit
autocommit = False: disable autocommit (the default)
autocommit = None: do not change the MySQL connection default

And also I need to save the autocommit state somewhere in the connection object for something else I have planned. The current value can be obtained with SHOW SESSION VARIABLES LIKE 'autocommit' which will be either "ON" or "OFF".