Bug fixes

Fixed issue where 0x00EE opcode wasn't incrementing the program counter.
Added in sound and delay timer decreases.  Set program counter to be
initialized at 0x200.  Added test for memory.getOpcode() and fixed issue
where the opcode was returning wrong.
Cpu bug fix

Fixed issue where drawX and drawY could be out of the bounds of the
screen, cause an ArrayOutOfBoundsException.