out_ptr/inout_ptr for all smart pointer types

Dear Boost.SmartPtr authors:

(This issue is a [continuation of the discussion from Boost.Move](https://github.com/boostorg/move/issues/22).)

My name is JeanHeyd and I am looking to make my [std::out_ptr / std::inout_ptr type that I am proposing to the standard](https://thephd.github.io/vendor/future_cxx/papers/d1132.html) more widely and publicly available. I was given the advice to put it in Boost in some fashion, and I realized that rather than making a new library contribution it would be better off if this was put in one of the 2 smart pointer-containing libraries, Boost.Move or Boost.SmartPtr.

The author of Boost.Move has stated that it seems like a better match for Boost.SmartPtr, and I agree: therefore, I am proposing to add 2 new templated functions and 2 new templated classes: `boost:out_ptr( ... );` and `boost::inout_ptr( ... );` alongside `boost::out_ptr_t` and `boost::inout_ptr_t`.

I wanted to know if this was acceptable to the library maintainers here, and if so I would begin to move the current implementation into Boost.

If it is not acceptable, I understand.

If it is acceptable, I would like to know what version of C++ Boost.Smartptr targets and any other caveats I should be careful of when crafting my first pull request. I can do a C++11 implementation without the need for workarounds, but C++03 will require some finesse.

Please do let me know what you think! I eagerly await your response.

Sincerely,
JeanHeyd