Start of a text.dat editor

Right now it's just a text.dat browser, but it's already somewhat
useful, so I'm comitting it.

Up/Down         = Change entry
CTRL-G          = Go to entry by number
PageUp/PageDown = Change output method (putmsg, mnemonics, print)
Q               = Quit
Left/Right      = Move the cursor around in the source text

This must be ran from the terminal server, it's really not reasonable
to do a text.dat editor as stand-alone.