described headers in docs; added move in operator>>

include/boost/optional/optional_io.hpp

@@ -62,7 +62,11 @@ operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v)
     {
       T x;
       in >> x;
+#ifndef  BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+      v = boost::move(x);
+#else
       v = x;
+#endif
     }
     else
     {