o Add setTables() method to ROMFile which allows each mapper to change
  the nametable mirroring directly.  This allows the removal of the ugly
  RefreshTables() mechanism that was used previously.

o Add interface MemoryTracer and MappedMemory.AddTracer method which is
  used by MMC3's scanline counter to see all fetches/stores on the PPU's
  address bus.