Workaround MSVC 16.20 bug. (#111)

Fixes #92.

Author: NN---

include/type_safe/reference.hpp

@@ -568,7 +568,7 @@ class function_ref<Return(Args...)>
     /// \exclude
     template <typename Return2, typename... Args2>
     function_ref(Return2 (*fptr)(Args2...),
-                 typename detail::enable_matching_function<decltype(fptr), Return, Args...>::type
+                 typename detail::enable_matching_function<Return2(*)(Args2...), Return, Args...>::type
                  = 0)
     : function_ref(detail::matching_function_pointer_tag{}, fptr)
     {}
@@ -617,7 +617,8 @@ class function_ref<Return(Args...)>
     /// std::string`, even though such a conversion would be ill-formed otherwise. \param 1 \exclude
     template <typename Return2, typename... Args2>
     explicit function_ref(const function_ref<Return2(Args2...)>& other,
-                          detail::enable_matching_function<decltype(other), Return2, Args2...> = 0)
+                          detail::enable_matching_function<const function_ref<Return2(Args2...)>&,
+                                                           Return2, Args2...> = 0)
     : storage_(other.storage_), cb_(other.cb_)
     {}