add dependency to the end of linked list
    Dependency *new_dep = malloc(sizeof(Dependency));
            new_dep->next_dep = NULL;
            
            //append dep. at end (or edge-case when empty)
            if(rule->dependencies == NULL){
                rule->dependencies = new_dep;
            } 
            else {
                Dependency *curr = rule->dependencies;
                while(curr->next_dep != NULL){
                    curr = curr->next_dep;
                }
                curr->next_dep = new_dep;
            }