Changelog:
* Added 4:3 (fit screen height) stretch mode, visible in NTSC mode or when border is disabled
* Added border toggle - shows/hides the border surrounding the main display area
* Added PAL/NTSC/Old NTSC mode selection
* Added vertical blanking (VSync) support, only available in NTSC mode
* Bugfix: PRG loading now works
* Bugfix: "fit screen" stretch mode aspect ratio was incorrect; now fixed
* Minor fixes