implement pooling

like https://dev.mysql.com/doc/connector-python/en/connector-python-connection-pooling.html
new option like MySQL connector :

• pool_name
• pool_size

other option I would recommend :

• acquireTimeout : timeout to get a new connection
• minDelayValidation : When asking a connection to pool, the pool will validate the connection state with a ping command. "minDelayValidation" permits disabling this validation if the connection has been borrowed recently avoiding useless verifications in case of frequent reuse of connections. 0 would mean validation has to be done each time the connection is asked.