plz note:  actually the lights just change color all the time because
the lights are being reflected back at the light sensor by the
enclosure.

this makes for an accidentally pretty great party mode, but isn't quite
what i was going for in general.

I don't know that this is actually helping, but it might be.

https://learn.adafruit.com/a-neopixel-blinkendisc/software

Notes:

I'm getting some kind of weird (timing-related?) thing where a couple of
pixels show up the wrong color.

Reacting to temperature probably isn't going to be all that interesting,
at least not like this.

Copying edited files to the mountpoint rather than editing directly on the
board kinda seems like the way to go.  Slightly laggier dev cycle, but a
little more deliberate.

Stole get_color_in_range() from a Stackoverflow answer.  Probably going to
get rid of it.

Haven't yet tried driving an external neopixel ring.