DRY for the operand_op_xxx() functions.
DRY for the operand_op_xxx() functions.

Created macros for OPERAND_BINARY_OP() and OPERAND_UNARY_OP().  These
contain the repetitive code that processes each operation.  Then each of
the operand_op_xxx() functions calls the correct macro.

joeriggs/calculator,joeriggs/calculator