Classes result in build warnings; build failure on Windows

[adetaylor]

A struct with methods gets processed nicely by bindgen, autocxx and cxx.

A class with methods results in compile warnings because:

• bindgen outputs a Rust struct
• autocxx passes struct-like information to cxx
• cxx generates C++-side bindings which include a forward declaration for this class... but calls it a struct. Therefore the compiler whines. Apparently on Windows this would actually be a bug due to ABI mismatch between structs and classes. (In the title of the issue I call this a 'build failure' but I'm not sure).

Currently the information output from bindgen doesn't tell us whether something is a class or a struct. We will need a small bindgen change to add a bit more information to the outputted code. I have a hacky branch for this; if anyone wants to clean it up let me know and I'll upload the hacks somewhere.

[adetaylor]

Taking another look here: this problem doesn't seem to exist any more. It might be that cxx has changed to no longer generate those forward declarations. I also now regret not adding a citation for the bit labelled "apparently" above: I'm sure I wasn't imagining it but I can't find it. I'll close this issue for now though I'm pretty confident it'll reappear.

[fzyzcjy]

Btw in README it says Works, except on Windows pointing to here. So if it is not a bug you may change the readme ;)