C65: review emulation precision (TEST!!), fixing things, missing parts (also helps Mega65!)

[lgblgblgb]

C65 emulator in Xemu is a much simple one (for sure) than Mega65. Though many features are in common. Also C65 emulator is in better shape. So it's a great place to experiment to make it even more perfect, where the code/knowledge/experience then can be used for the Mega65 emulator as well, also in addition, it can help make the C65-only emulator being even better, so double value for our money :)

Now I know of at least one missing feature: support of VIC-III's DAT (also missing in Mega65 emulation).

Also, try to test the C65 emulator with existing C65 software, if it's possible too much at all (not so much of them ...).

[lgblgblgb]

First test material now: K2 demo, see here: #142