From off:
  * 1 click: memorized level
  * Hold: Lowest level then ramp up
  * 2 clicks: turbo
  * Click, hold: highest level then ramp down
  * 3 clicks: battcheck mode
  * 4 clicks: lock-out
  * 5 clicks: strobe mode
  * 6 clicks: momentary mode (disconnect power to exit)

In steady mode:
  * 1 click: off
  * Hold: ramp up
  * Click, hold: ramp down
  * 2 clicks: to/from turbo
  * 3 clicks: toggle smooth vs discrete ramping
  * 4 clicks: configure current ramp

Smooth ramp config mode:
  - Setting 1: memory on/off
  * Setting 2: low end
  * Setting 3: high end

Discrete ramp config mode:
  - Setting 1: memory on/off
  * Setting 2: low end
  * Setting 3: high end
  * Setting 4: number of levels

Strobe mode:
  * 1 click: off
  * Hold: change speed (faster)
  * Click, hold: change speed (slower)
  + 2 clicks: next strobe mode
    (party strobe, tactical strobe, random/police strobe?, bike flasher)

Bike flasher:
  - 1 click: off
  - 2 clicks: party strobe
  - Hold: brighter
  - Click, hold: dimmer

Battcheck mode:
  * 1 click: off
  * 2 clicks: tempcheck mode

Tempcheck mode:
  * 1 click: off
  - 2 clicks: beacon mode
  - Hold: thermal calibration

Beacon mode:
  - 1 click: off
  - 2 clicks: battcheck mode
  - Hold: brighter
  - Click, hold: dimmer
  - 3 clicks: configure time between pulses

Momentary mode:
  * Press button: Light on (at memorized level).
  * Release button: Light off.
  * To exit, disconnect power.  (loosen/tighten the tailcap)

TODO:
  - save settings in eeprom
  - a way to blink out the firmware version?
  - a way to configure indicator LED behavior?