refactor: drop Boost.Move dependency

Implement constexpr definitions of forward and move to replace usage
of boost::move and boost::forward from the Boost.Move library.

Alter tests to use std::move instead of boost::move.

Remove the dependency on Boost.Move from build.jam

include/boost/optional/detail/optional_reference_spec.hpp

@@ -39,7 +39,7 @@ BOOST_DEDUCED_TYPENAME boost::remove_reference<T>::type& forward_reference(T&& r
 {
     BOOST_STATIC_ASSERT_MSG(boost::is_lvalue_reference<T>::value,
                             "binding rvalue references to optional lvalue references is disallowed");
-    return boost::forward<T>(r);
+    return optional_detail::forward<T>(r);
 }
 
 #endif // BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES