o Define NES type in nes.go.  Contains instances of rp2ago3.RP2A03,
  rp2ago3.MappedMemory, m65go2.Clocker and ROM.  Create a new NES with
  NewNES, passing it the filename of a .nes ROM file.

o Define new ROM interface with embeds the MappableMemory interface.

o Added new ROMFile type which represents the data stored in an iNES ROM
  file.  Path NewROM a filename to a .nes ROM file and it hands back a
  ROM instance.

o Add NROM type which implements the ROM interface.  NewROM will return
  an NROM instance if the iNES header indicates the ROM uses mapper 0.