Note some recently observed bugs
Set a bigger default size
Don't let zoomer window be resized
Don't allow keyboard movement outside image bounds
Improve image loading speed

The setPixel() method is way too slow for updating all the pixels, this
method is much faster. This also improves startup speed when loading an
image from the command line.
Change display range
Ignore mouse/key events if no image loaded
Activate/deactivate some menu entries
Clip image properly

Otherwise, during the conversion to uint8, the values are wrapped around
and aliased.
Update documentation and changelog