Figure out a plan for functions that return references but take more than one reference

[adetaylor]

cxx allows C++ functions which return references, but only if they take exactly one reference parameter (since then the lifetimes are obvious).

As our hope is to handle existing C++ APIs, we will encounter functions which return references and take 0 or 2+ reference parameters.

If they're methods, autocxx may try to generate them even if they're not in an explicit generate list.

So, we either need to silently skip them, or find some way that their behavior can be made unambiguous in a directive within the include_cpp! macro.

[Volker-Weissmann]

One could add lifetime specifiers by adding machine readable comments in the C++ function signature.
Or have those lifetime specifier in a seperate file.

If none of the above exists, then autocxx should return a raw pointer.