o Use commas to separate switch case statements with the same action
  instead of using 'fallthrough'.

o Enable PPU decoding with new ppu.ToggleDecode method.

o Clear VBlankStarted, Sprite0Hit and SpriteOverflow flags on cycle 1 of
  scanline 261 regardless of whether rendering is enabled.  This stops
  Zelda from hanging after pressing Start at the title screen.