o Delete CPUer interface, it isn't really necessary since RP2A03 just
  embeds M6502.

o Modified NewRegisters to call Reset() on itself

o Added breakError field to M6502 type, used in tests so BRK
  instructions will kick us out of Run()

o Moved NTSC/PAL_CLOCK_RATE out of this package and into rp2ago3

o Modified M6502.Reset() to set the PC register to the address in the
  RESET vector (0xfffc/0xfffd).

o Added Irq() method to M6502, not used anywhere yet.