Right now all of the element code uses port indexes as unsigned integers. Originally this was to match what LV2 itself is doing. To make life easier, we should use signed 32bit integers to represent a port. This will cut way down on casting back and forth from signed/unsigned.

These do not need to be public. Do this by making it a private class of DigitalMeter

At the moment, meter value objects are stored and released in a naked pointer array. This is fine and working, but we want to move toward using smart pointers/arrays as much as possible to avoid potential memory leaks and other problems.