Multiplication by the complex conjugate : mult_c_conjugate

### 2.11.9 Multiplication by the complex conjugate :
`mult_c_conjugate`

`mult_c_conjugate` takes as argument an complex expression.
If this expression has a complex denominator, `mult_c_conjugate` multiplies the numerator and the denominator of this expression by the complex conjuguate of the denominator.
If this expression has not a complex denominator, `mult_c_conjugate` multiplies the numerator and the denominator of this expression by the complex conjuguate of the numerator.
Input :

`mult_c_conjugate((2+i)/(2+3*i))`

Output :

`(2+i)*(2+3*(-i))/((2+3*(i))*(2+3*(-i)))`

Input :

`mult_c_conjugate((2+i)/2)`

Output :

`(2+i)*(2+-i)/(2*(2+-i))`