Implement non-squeezed side-by-side mode

This patch resolves #44. However, it currently does not automatically send "resize" event to Blender, so after pressing "d" to enable/disable stereo 3D (or after toggling "Full Width" when stereo 3D already enabled) you need to resize Blender window by at least 1 pixel (or toggle/untoggle fullscreen). I did not figured out yet how to send Blender "resize" event (without resorting to changing window size). Perhaps you have an idea?