Add support for Motorola 6800 and 6809

[Bananattack]

The Motrola 6800 and 6809 should be closer in spec to existing systems, and should be easier to support than the 68000 for example, as the instruction set has much simpler rules and less possibilities.

This would allow support for systems such as:

• APF Microcomputer System / APF-MP1000 (6800)
• TRS-80 Model I (6809)
• Vectrex (6809)

These instruction sets are pretty different but apparently "source level compatibility" was possible for 6800 assembling programs on 6809, so there might be some overlap. It sounds like the instruction encoding and capabilities shifted around, but a lot of 6800-equivalent functionality was possible on a 6809, which was strictly more powerful.

Not a priority, but could be nice some day.