Scale functionality should be separated

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This repo should focus solely on communicating with a HX711. Functionality built on top, such as a scale for measuring weight, is out of scope and should be removed/moved into its own repo.

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A rpi-scale-cxx repo should be created for the scale functions.

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Classes to be removed:

AbstractScale Mass Value ValueStack

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On second thought, having scale functionality as part of a "library" should persist, but should be more clearly separated from the base HX711 functionality.