title: Atomic operations on `unique_ptr`
body: <p><code>std::shared_ptr</code> <a href="http://en.cppreference.com/w/cpp/memory/shared_ptr/atomic">has specializations for atomic operations</a> like <code>atomic_compare_exchange_weak</code> and family, but I cannot find documentation on equivalent specializations for <code>std::unique_ptr</code>. Are there any? If not, why not?</p>