6502: copy Ozmoo's homework

[susan-davis]

Ozmoo (and ozmoo.online) supports a number of features that the Å-machine doesn't:

• support for the C128, C64 REU, Plus/4, MEGA65, and Commander X-16
• detection of the presence of a REU
• adjustment of the interpreter's default colours
• choice of the shape and blink rate (or lack thereof) for the cursor
• switching back and forth between "dark" and "light" modes (two user-defined colour schemes) with a single keystroke
• support for multiple disk drives, and for building disks for the 1571 and 1581
• UNDO and scrollback buffers in the REU or a C128 RAM buffer

Ozmoo is also open source, so all of the above has been written in 6502 assembly and is available to steal adapt for the Å-machine, much faster than writing all of that from scratch would be. There's also a Z80 version for the Acorn Archimedes, if we're ever feeling that ambitious.

(It's also a nice question whether simply adding .aastory support to Ozmoo would be faster than scavenging Ozmoo features for the Å-machine 6502 runtime would be.)