Speed optimizations (IEC bus)

[dirkwhoffmann]

This comment has been dangling around in config.h for a long time. I'm making an issue out of it so it can be deleted from the source code:

// IDEAS:
// Update IEC bus inside CIA and VIA. Use delay flags if neccessary.
// Call CA1 action in VIA class only if the pin value really has changed.

[dirkwhoffmann]

The IEC bus is now updated by scheduling an IEC_UPDATE event in the IEC slot:

The CIAs are also driven by the event scheduler now (like in vAmiga).

I've also refactored C64::execute() quite a lot, resulting in cleaner code. Unexpectedly, the new code does not bring any speed improvements.

[dirkwhoffmann]

Fixed in v4.7b1