nixie_tubes mod by Vanessa Ezekowitz

This mod provides a set of classic Nixie tubes, controlled by Mesecons' 
Digilines mod.

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

Then send a message to that channel from a Mesecons Lua Controller with either
a number 0-9, the word "colon", the word "period" or the word "off".  The tube
will "light-up" the appropriate number or symbol, or turn off entirely.

Tubes emit a small amount of light when displaying something.