Replaced optparse with argparse, since the first one is deprecated and replaced with the latter.
Major rework in case of resizing pictures. The window get a fixed size and pictures are resized to fit into it. Scaled down the zoom steps
Get zoom_percent on actual window size.
Change retrieval of initial window size. Avoid odd pixel sizes. Default to 800x600.
Change behaviour of get_zoom_percent. Remaining issue since a few commits: Change to fullscreen --> doesn't update zoom_percent. if changed back it takes the value of fullscreen, minimizes the screen and updates zoom_percent to the value necessary for fullscreen.
Resolve issue reported with 155bf46. Make sure that switching to fullscreen and back doesn't confuse the calculation of the zoomfactor.
Support multiframe pictures. Most stuff is needed to avoid a scale call since the Animation module doesn't seem to have something similar.
0.4.0
0.4.1: Fixed bug where changing the zoom or similiar actions that would just update the image and won't move the index up an down caused a problem with the pixbufOriginal was already changed but still checked if it's an Animation object.

ToDo: Looking for a cleaner way to do the check?