Addition and Subtraction: New Instructions

New CPU status flags:
carry flag,
overflow flag, 
negative flag.
New instructions!
CCLR : Clear Carry flag
CSET : Set Carry flag
JPCC : Jump Carry Clear
JPCS : Jump Carry Set
JPVS : Jump Overflow Set
JPVC : Jump Overflow Clear
JPPL : Jump if Result Positive
JPMI : Jump if Result Negative

Modify ADD and SUB to use the carry flag rather than an ALU signal.
Write the abstract RTL.  
Add logic to generate the new flags
Write concrete RTL