No error state handling

[corygrant]

Use an enum state machine to control what is possible in each state and how to get in/out of each state.

• POWER_ON
  • Check comms to all devices
  • FRAM
  • Temp sensor
  • ADC DMA
  • USB CDC
  • Status LED off
• STARTING
  • Read config from FRAM
  • Status LED off
• RUN
  • Check board temp
  • Overcurrent shouldn't trigger an error state
  • Should battery under/over voltage trigger some kind of error state?
  • Severe errors should change state to ERROR
  • Status LED on solid
• OVERTEMP
  • Wait until temp drops before resetting back to RUN
  • Flash the Status LED quickly to indicate OVERTEMP
• ERROR
  • Require power cycle?
  • Severe errors are not likely to be cleared on their own
  • Come up with error code number scheme
  • Flash the Error LEDs based on error code

[corygrant]

Added device state and error handling in 2e685276f51f1e7278cc545c68bdf57086686d8b and f9157fb374f78c04b4cf4d37540b34e4a51efad3