Port test program to i8080-only instructions
Remove implementation of Z80-specific instructions
Remove N status flag
Remove registers I, R, IX and IY
Remove some left Z80-specific instructions
Remove Z80-specific ALU code
Fix arithmetical ops to set PV status to parity instead of overflow
Remove isOverflow()
Rename PVstatus flag to P
Remove second set of registers (Z80 feature)
Merge branch 'z80-cleanup'