Cache and reuse generated tokens.

[floor114]

Closes #3

[matt-domsch-sp]

Since this requires seting reconnect false to the low-level mysql C connection layer, what is the behavior when a database cluster fails over from primary to replica, promoting the replica, and a previous connection no longer works? Today, without using thsi gem, the low-level driver reconnects automatically, invisible to the application. I'm concerned that not setting this, that activerecord won't automatically reestablish a connection.