Fix LSR so that it writes result to memory/accumulator. Implement NMI/IRQ handlers. Fix status flag code so that Unused and BrkExecuted are never set on P, but only pushed to stack.
Add write support to FileStream
Debugger: add 'd' to dump memory to files (cpu, ppu, sprite).
PPU signals a single NMI when CPU enables NmiOnVBlank, which gets the title screen of Donkey Kong into VRAM