New firmware for 4.6 board support

- Adds support for the mode button to cycle modes
- Adds support for volts
- Adds support for water temp
- EFI is
    - solid for EFI error
    - slow flash bad ECU comms
    - fast flash for water temp too high
- Includes our own SWSerial7800 library which is just AltSoftSerial
  but with 7800 baud support so people don't have to modify their own
  library for Arduino UNO boards
- Add dbg_serial_printf() for cleaner code & debugging

TODO:
- Need to make sure voltage calculation is accurate
- Add Low Fuel light support
- Improve mode button responsiveness?