Add querying offsets #38
Description
A feature that would be helpful for me would be reflecting over member offsets, as this would allow use cases like automatic generation of vertex attributes in graphics programming for example. I've managed to hack together something for the VISITABLE_STRUCT macro, however I believe this is not possible to implement intrusively as this would require getting the offset of an incomplete type.
I don't fully understand how the templates etc work so I imagine it won't be optimal, but I did manage to hack something together, so I'll add a pull request for review.