game demos

[Juhász P. <pet...@gm...>]

Dear gnuplot list,

by popular demand ;), I've added the game demos discussed earlier to the
CVS.

Fixes: 
- up key now disabled
- key events are now handled after the pause so they don't mess up the
internal state
- label size chosen according to terminal

Standing issues: 
- with the wxt terminal, keypad + and - appears to keep their default
functions, even though they are rebound explicitly by the script

Please waste time by playing them^W^W^W^W^Wtest them thoroughly!

Peter