PS2KM - Further developments

The code for ps2km is ready to put into a prototype system. This will be done over the coming days.

More ideas for the ps2km include classic and wheel startup modes, selectable by different mouse button combos on power-up/reset.

Classic mode will disable the scroll bits so the buttons byte will work as a normal kmouse (inactive bits are high).

Wheel mode will enable the scroll bits (if the connected mouse has a wheel).
Bit 3 (Z Change) will be 1 for no change. 0 for change present.