#64 easy changing (shortcut) for font size

[Markus]

Make some common shortcut for text "zooming" (increasing / decreasing font size) available for gVim - because sometime you need a smaller font size for more overview and sometimes you want a big font size which is easier on the eyes..

A common and widely used short cur for this purpose is Strg + / Strg - (used on all Mozilla Products, in consoles in Gnome and KDE and much more widely used software). The behaviour should be like it is on these examples.

Its only needed for gVim, because if you are using vim on a graphical console you can use their shortcut for this purpose, and on the real console you can use a shortcut for "consolechars" or sth. like that.