Method emplace

src/fl/stl/multi_map.h:329–334

    template<typename... Args>
    iterator emplace(Args&&... args) {
        value_type temp(fl::forward<Args>(args)...);
        ValueWithId vwid(fl::move(temp), mNextId++);
        auto result = mTree.insert(fl::move(vwid));
        return iterator(result.first);
    }

    // Range insert
    template <typename InputIt>