Expand c++ stdlib support

[anderslanglands]

Currently there is basic support for std::vector by wrapping it as an opaquebytes type which can be passed around. This seems to work quite well, despite being quite unsafe. It's currently named cppmm_vector but this should probably be changed to std_vector for consistency. Support for destroying these objects also needs to be implemented (just needs a _drop function probably).

Once that's done we should add support for other stdlib types. So far I've only seen std::set in an API (in USD) but I don't doubt there are others out there as well.

[luke-titley]

Is it not possible for the stl types to be exposed in the same way that the wrapped library bindings will be exposed ?

[anderslanglands]

That could potentially work, but it means adding stdlib to the list of supported libraries, rather than just special-casing certain types and handling them directly.

At this stage I'd much prefer to write dedicated support for the containers that we need than to try and make a general solution.