New release V1.4

Uploaded New Release v1.4:

Rewrited the function:

double AddVar::partial_derivative(const std::vector<Var*>& V, int Var_i, int VarNum);
//use a more accurate way to calcutale partial derivatives

Add new funciton:

void AddVar::AllPartial(const std::vector<Var*>& V,int VarNum);
//Form a table, showing all the partial derivatives of an added variable