Fix hundreds of improper_ctypes warnings

[Ameliorate]

This does it by adding a 8 bit padding value to the lua_State struct.

These warnings, however, are still correct. The C spec does not account for zero sized structs. In C, structs that are empty still take up space, for the reason that two different variables will always have different addresses.

[tomaka]

The struct is only ever accessed by pointer, so in theory it's not a problem if it's zero-sized. I'm not sure if your PR is the right fix to these warnings.

[Ameliorate]

You do have a point. The issue could also be fixed by having a

![allow(improper_ctypes)] on the module root.

[TyOverby]

@Ameliorate Or a #[allow(improper_ctypes)] on the struct itself.