code: public static ComplexNumber Add(ComplexNumber z1, ComplexNumber z2) {
          return new ComplexNumber(z1.real + z2.real, z1.imaginary + z2.imaginary);
      }
docs: Adds two complex numbers.
  
  @param z1 Complex Number.
  @param z2 Complex Number.
  @return Returns new ComplexNumber instance containing the sum of specified complex numbers.