First class `std::array` support

[dmillard]

Using CxxWrap.jl is really smooth and it's exceptionally well built, thank you!

I don't see a clean way to wrap std::arrays in a generalizable way. I'm currently wrapping individual instantiations with a similar setup to that mentioned in JuliaInterop/libcxxwrap-julia#90.

Is there any feasible path forward for a general std::array wrapper? If so, could it be included in CxxWrap.jl? If not, maybe it could be useful to include a facility for wrapping individual instantiations that "play nice" with the Julia array interfaces.

[AUK1939]

Looks like there are only 3 stl containers currently supported in libcxx_wrap (vector, valarray and deque). Would be good to have std::set support aswell.

I guess this is related to #190

[barche]

Yes, contributions to add more STL support are most welcome!