Brief update

I've identified the main game loop, the keyboard read routines, and commented most (95%) of the movement routines - definitely enough to start porting and see the results.

There's a decent amount of code that needs to be written before I'll see the player moving around on the screen. It's probably not something that can be written in a single session. I also need to properly implement the dual screen logic as it is used extensively in the movement code, for example.

For this reason, I've decided to update the Coco3 (6809) port first. It's a bit simpler than the TRS-80 port since for the latter I'll need a shadow copy in RAM of the port-mapped hires screen, and hence I'm unable to make use of dual-purpose routines. The latter is also slower and more painful than the 6809 port - so much so that I'm actually tempted to put it on ice for the moment.

Next time I sit down to work on this I'll be able to start on the Coco3 port!