Remove function

    if (empty())
        return false;
    else if (index>=size_)
        return false;
    else if (index==0){
        remove_front();
    }
    else if (index== size_-1){
        remove_back();
    }


    else {
        Node* n1=getNode(index);
        getNode(index+1)->prev=getNode(index-1);
        getNode(index-1)->next= getNode(index+1);
        delete n1;
        n1= NULL;
        size_--;
        return true;
    }