nixie_tubes mod by Vanessa Ezekowitz

This mod provides a set of classic Nixie tubes, and a set of alphanumeric
15-segment tubes similar to Burroughs B-7971, controlled by Mesecons'
Digilines mod.

Simply place a tube, right-click it, and set a channel.

Then send a character or one of several control words to that channel from a
Mesecons Lua Controller and the tube will try to display it.

The classic tubes are numeric with colon and period symbols, and hence will
respond to the literal numbers 0-9, and the words "colon", "period", and
"off".  Any other symbol or word is ignored.

The alphanumeric tubes respond to characters from the standard 7-bit ASCII
character set, along with these messages:

* "off", "colon" and "period" act the same as on the numeric tubes.  Note that
  neither a colon nor a period actually look all that great on a 15-segment
  display, so use a classic tube for those, if you can.
* "del" or character code 127 displays an all-on square, but without segment
  #15 (the bottom, chevron-shaped one).
* "allon" or character code 128 will display an all-on square, with segment
  #15 lit also.
* "cursor" or character code 129 will display just segment 15.

Any unrecognized word or symbol outside the 32-129 range is ignored.

Tubes emit a small amount of light when displaying something.