lua-getsize/luatraverse for 5.2+

[Matthew Wild <mwild1@...>]

Dear Lua community,

Over 10 years ago I wrote a tiny C module[1] that allowed you to get
the size of a Lua object in bytes. This was quite handy for debugging
memory usage, especially when used in combination with luatraverse[2],
originally written by Alexandra Barros back in 2006.

Unfortunately both projects were developed for 5.1 and don't work
(correctly) under more recent Lua versions.

I don't currently have the time to update either project. But I
wondered if anyone in the community had any alternative code for doing
the same, would feel inclined to spend some time on this for the good
of the community? <3

Regards,
Matthew

[1]: https://code.matthewwild.co.uk/lua-getsize
[2]: https://code.matthewwild.co.uk/luatraverse