Add VIC20 support

[ricardoquesada]

From a msg that I received:

Another thing, would you consider adding support for VIC 20? Things to adjust:

• Different palette: No grays. 0-7 same as C64, 8: orange, 9: light orange, 10-15 are bright/light versions of 2-7
• Different pixel ratio (0.750 flat is close on NTSC, 0.800 something on PAL)
• Other one of the two multicolor values is also the border color
• Multicolor pixel pairs are mapped differently from C64
• Switchable 8x8 or 8x16 character mode. In 8x16 mode you can address 256 chars, covering twice the amount of pixels compared to C64

[AndyHOvine]

Would love Vic 20 support! All the ideas above would work great.