Provide interoperability between std::chrono::duration and boost::units::quantity<time>

[jpo234]

The time dimension is special in C++, because there already is an implementation in the standard libraries: std::chrono::duration.
I think boost::units should recognize this and provide an easy way to convert between these two different implementations of what is basically the same thing.
Ideally one should be able to do:
quantity<time> q = 2h;
where 2h is a std::literals::chrono_literals::operator""h.

[correaa]

Yes, one problem is that chrono is based on integer value types while Boost.Units, is generally based around floating point values. But I would also like something in this direction.