Add borders (color background) option

@carmiker

Borders (Color Background) Enable this to display the overscan regions at the top/bottom and/or left/right of the screen. These would normally be hidden by the bezel around the edge of a standard-definition television

OFF Left/Right Top/Bottom (NTSC/Famicom mode) Top/Bottom (PAL/Dendy mode) Full (NTSC/Famicom mode) Full (PAL/Dendy mode)

It's not out of the question, but this is fairly low priority. The major focus of my work on Nestopia will be passing all of the TASVideos accuracy tests.