Auto surface

Once Tanny has submerged, and remained so for 10 seconds, it must surface. It needs to know what submerged is, and it needs to count time.

Suggest

Once an attempt at submersion starts, count on a dive timer. Once near-submersion is attained, count on a submerged timer. Don't stop counting unless submersion mode is cancelled. The timers can be on an interrupt loop.

Cancel for these reasons:

1. Once 15 seconds of submersion has been counted.
2. If an attempted submersion takes more than 20 seconds.
3. If terminated remotely