added NaN test for operator_addition
added failing NaN test
fixed agrad/rev/operator_addition so gradient returns NaN for NaN inputs
added NaN test for operator_division
added failing NaN test
fixed operator_division so gradients return NaN for NaN inputs
added NaN test for operator_multiplication
added failing NaN test
fixed operator_multiplication so gradients return NaN for NaN inputs
added NaN test for operator_subtraction
added failing NaN test
fixed operator_subtraction so gradient returns NaN for NaN input
add NaN test for operator_divide_equal
fixed NaN test for operator_divide_equal
added NaN test for operator_multiply_equal
fixed NaN test for operator_multiply_equal
added NaN test for operator_unary_decrement
added failing NaN test
fixed operator_unary_decrement so gradients return NaN
added NaN test for operator_unary_increment