[Coco] WIP - RGB2VGA 800x600

[CoCo Demus]

Hi all RGB2VGA makers,

This is experimental and has not been tested in more than 2 monitors (the
ones I have here).

But this code below gives you 800x600 output. No modification needed, just
upload the code below using quartus/usb blaster.

It's the .sof (temporary) yet but when finished I will publish a branch on
github with the .jic

https://sites.google.com/site/tandycocoloco/dropbox/rgb2vga.sof?attredirects=0&d=1

The screen gets smaller, there is no stretch algorithm but you get the full
borders around and not problem with overscan too left or too right.

Check also the color stability. You can play predator or rampage and check
the beautiful stable colors. There is a small residual jitter on 80 colum
mode (if compared to the current head version in 640x480) but still very
good.

This is due to QuartusII 15.0 be able to generate a better and optimized
code.