Beginning to rework the VIC-IV to support DMA delay and other things

Until now, the VIC-IV implementation has fetched the character and colour ram byte as it draws each character.  Also, it has basically been hard-wired to fetch characters from

This has been fine for testing text mode things, and also for the new full-colour graphics mode I added, which is really just text mode on steroids, with characters composed of 64 8-bit colour values.

But now I want to get bitmap mode to work, so that at least technically simple graphics can work.  Similarly, it would be really nice for custom character sets to work.

To give an idea of what happens now, see the following screen shot of the crack intro to labyrinth.

My poor old phone camera has trouble capturing the motion, but you can see that the $D016 horizontal smooth scrolling is doing something.  In fact, it is working just fine on the live display.  However, as mentioned above, everything is just using the ROM-based character set, instead of showing what it should.

So the next step is to get it reading character and bitmap data so that things display correctly.

After that, it will probably be working on latching character and colour data for an entire character height, so that it more closely matches VIC-II/VIC-III behaviour.