devtimer / TODO
- Cleanups:

  - Collect globals into a more coherent centralized namespace
  - Cleanup debug handling using that centralized state info
  - Cleanup timer run code into separate thread that gets started/stopped instead of always running with 0 displayed

- Autodetect temp probe device
- Generate compensation tables at startup based on low/hi range - perhaps limited by times <400ms
- Speed up boot time by removing all unneeded boot activity
- Package into a preconfigured DD image for release simplicity
- Longer term: Move to an SPI based set of displays for better rendering speed.