Cannot deal with reference_wrapper

[Quuxplusone]

I would expect this test case to pass:

TEST_CASE("issue 67") {
    int i = 42;
    int j = 43;
    tl::optional<std::reference_wrapper<int>> a = std::ref(i);
    REQUIRE(&a.value().get() == &i);
    a = std::ref(j);
    REQUIRE(&a.value().get() == &j);

    tl::optional<int&> b = std::ref(i);
    REQUIRE(&b.value() == &i);
    b = std::ref(j);
    REQUIRE(&b.value() == &j);
}

Instead, it currently fails to compile:

tl-optional/include/tl/optional.hpp:1942:41: error: cannot initialize a member subobject of type 'int *' with an rvalue of type 'std::reference_wrapper<int> *'
  constexpr optional(U &&u)  noexcept : m_value(std::addressof(u)) {
                                        ^       ~~~~~~~~~~~~~~~~~
tl-optional/tests/issues.cpp:55:28: note: in instantiation of function template specialization 'tl::optional<int &>::optional<std::reference_wrapper<int>, nullptr>' requested here
    tl::optional<int&> b = std::ref(i);
                           ^

Furthermore, I'd like the following to compile too:

    tl::optional<int&> c = a;
    REQUIRE(&c.value() == &j);
    c = tl::optional<std::reference_wrapper<int>>(std::ref(i));
    REQUIRE(&c.value() == &i);

But that requires solving issue #66 first.