Add 'size' and 'position' to windows terminal options

[Benjamin L. <lin...@gm...>]

Hello,

I'd like to propose the addition of a 'size' and 'position' option
to the windows terminal.
This would fit very nicely in the possibility to position the
plotting figure from octave on screen when using the gnuplot plotting 
backend.

I attached a patch which accomplishes it.
Comments?

benjamin