Update vram addr in the pre-render scanline
Don't increment Y if rendering's not enabled
Forgetting to update the PPU in both the CPU's memory and the machine when stepping it
Add chr RAM to NROM

If there are 0 chr-banks then it should use RAM on-board the cart
instead.
Actually handle interrupts
Broke specs by assuming chr ram is always {}, this fixes that
Able to select the right tiles and pixels within them to render based on the PPU's VRAM addr
Render the background pattern to a buffer