o Modified M6502.PerformInterrupts to return 7 cycles for each
  interrupt.

o Modified M6502.Execute to add cycles returned by PerformInterrupts to
  the total cycles executed.

o Modified how bits 4/5 (unused/B flag) of Status (P) register and I
  flag are set/retrieved by PHP, BRK, /IRQ and /NMI based on

  http://wiki.nesdev.com/w/index.php/CPU_status_flag_behavior

o Add Execute method to InstructionTable, used by M6502.Execute.  Takes
  into acount page crossing/successful branches to determine correct
  cycle count for each instruction.

o Added support for a number of unofficial instructions: ANC, ALR, ARR,
  AXS, SHY, SHX.

o Initialize all memory to 0xff by default instead of 0x00 in
  BasicMemory.Reset.

o Disable overscan by default in SDLVideo.

o Zero top 2 bits of color in RP2C02.renderVisibleScanline as they are
  ignored by the hardware and cause array index out of bounds errors if
  set.