More resizing feature suggestions

[Lascaille]

Hi Nils - thanks so much for accommodating my feature request to add resizing to + and - on the numpad.

I have a couple more suggestions along the same lines:

1. Picaview and ACDSee responded to ' * ' as 'best fit' and ' / ' as 100%. I know I suggested 'enter' to switch modes but if you really want follow the spirit of it... :)
2. ACDSee interprets both ' + ' and ' = ' as 'zoom in' and both '_ ' and ' - ' as 'zoom out' to accommodate users without a numpad, who would otherwise have to press ' shift = ' to get the ' + ' symbol. Could be good to add the extra keys if it's only a couple lines.
3. Window resizing when zoom levels are changed - It seems that the window resizing procedure takes place in two steps. First the image expands to the bottom right (the top-left corner of the window does not move) and then the window is moved to the center of the screen. The result of this is that the window is drawn twice - you can actually see it being redrawn and then moved. Is it possible to do it in one step? Should also speed things up as the window only has to be drawn once...

[Lascaille]

Not really having a lot of experience with c++ but I forked this and I've made the window redrawing a whole lot faster. I've introduced a scrolling bug though (zoom in a lot, scroll, zoom out = problem) so wouldn't recommend you pull it :)