From off:
  * 1 click: memorized level
  * Hold: lowest level then ramp up
  * 2 clicks: highest ramp level
  * Click, hold: highest level then ramp down
  * 3 clicks: battcheck mode
    (battcheck, tempcheck, then beacon?)
  * 4 clicks: lock-out
  * 5 clicks: strobe modes
    (bike flasher, party strobe, tactical strobe, police strobe?)
    (remembers which you last used)
  * 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 (actual turbo, not just highest ramp level)
  * 3 clicks: toggle smooth vs discrete ramping
  * 4 clicks: configure current ramp

Smooth ramp config mode:
  - Setting 1: memory on/off  (not implemented yet)
  * Setting 2: low end
    (click N times to set ramp floor to level N)
  * Setting 3: high end
    (click N times to set ramp ceiling to level "151 - N")

Discrete ramp config mode:
  - Setting 1: memory on/off  (not implemented yet)
  * Setting 2: low end
    (click N times to set ramp floor to level N)
  * Setting 3: high end
    (click N times to set ramp ceiling to level "151 - N")
  * Setting 4: number of levels in discrete ramp
    (click N times to make discrete mode have N stair-steps)
    (minimum 2, maximum 150)

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

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

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

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

Thermal config mode:
  * At buzz, click N times to set thermal limit to roughly 30 C + N.

Thermal calibration mode:
  - Hold until hot: set new ceiling value
  - ... don't hold: blink out current ceiling value and exit

Beacon mode:
  * 1 click: off
  * 2 clicks: battcheck mode
  * 3 clicks: configure time between pulses

Beacon config mode:
  * At buzz, click N times to set beacon frequency to N seconds.

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
  - decide on "hold until hot" or "click N times" for thermal config mode
  - test thermal regulation on an actual light
  - improve thermal regulation
  - a way to blink out the firmware version?
  - indicator LED support
  - a way to configure indicator LED behavior?
  - add goodnight mode?
  - add lightning mode?