Support VidHD in slot 3 (via Config GUI or '-s3 vidhd') for SHR video modes only.
- AppleWin window is slightly enlarged when VidHD card is inserted.
Support IIgs 320x200 (and fill mode) and 640x200 video modes.
Debugger: add 'shr' command to view video
CUI: Allow user to specify width & height (for full-screen); and allow separate x,y scaling in full-screen mode.