CPU:
- LDY and LDX must behave properly in 8-bit mode when x bit in the p status 
  register is set to one
- Accumulator must behave properly when in 8-bit mode
- Emulation mode support in general.
- Have each operation return the number of cycles used by the execute function.
- updating the n bit of the status register
- Implement another 200+ operations
Memory:
- Banks
- ROM protection
- Memory mapped I/O