Added preliminary LD-V1000 emulation. Not fully working yet, but mostly
there.
Cleaned up and normalized the three existing laserdisc emulations.
Removed obsolete code from the laserdisc core.
Added new item to the interface which is the tag of a CPU
to take the base clock from. Are there any known cases
where the base clock does NOT come from the CPU directly?
Changed Z80 daisy chain interface to simply be a list of
devices in the chain. Interrupt callback functions are now
fetched via the standard device interface and referenced by
the daisy chain code.
Changed Z80 PIO interrupt callback to pass a device instead
of the machine. All device callbacks should provide the
device.
