Automatically SELECT database after HELLO?

[ysc3839]

Currently there's not an on_connect callback, so it would be helpful to execute SELECT automatically after HELLO.

[criatura2]

Good point. It would be even better if the HELLO command would allow SELECTing automatically since this is the first command to be executed.

[mzimbres]

This looks like an important addition, I will think more about where exactly it should be implemented. We can put it in the connection config so that if set it gets sent with HELLO.