IoT water tank telemetry project – ultrasonic sensor

The code developed for support of some ultrasonic sensors has been merged into the original tanklevel project at https://github.com/owenduffy/tanklevel. A lot of refactoring to provide to the change.

So far, support is provided for HC-SR04 (and things that emulate its PWM mode), MB1242 (and emulations like GY-US42v2).

A work in progress…