Function stringify

crawl-ref/source/playable.cc:69–74

template <typename Coll, typename S>
vector<string> stringify(const Coll &c, S stringify)
{
    vector<string> result;
    std::transform(c.begin(), c.end(), std::back_inserter(result), stringify);
    return result;
}

vector<string> playable_combo_names()
{