serialization for boost/optional

The boost serialization library includes an implementation for boost/optional. This breaks the general rule that serialization of boost components be implemented as part of that component and that only the boost serialization only contain implementations of serialization for std components. Now that there is a std::optional as part of C++17 we want to add another optional implementation to serialization. But on order to do that we want to move the current implementation here in order to "make room". I need to know if the maintainers of boost::optional are OK with this and will be willing to merge the PR. My inclination is to do this via a fork/pull request. Please let me know if this is all OK.