The docs make it seem like they are all things a single object
would implement. That's true of Driver and DriverContext,
but Connector is really something else. Attempt to clarify.

Change-Id: I8fdf1cff855a0fbe37ea22720c082045c719a267
Reviewed-on: https://go-review.googlesource.com/82082
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>