LuaJIT FFI Compatibility

[Pspritechologist]

Hello! I was hoping to get a clearer view of the compatibility between this library and LuaJIT's FFI API. I'm looking to migrate some LuaJIT code over and, obviously, it's not quite 1:1.

In particular, I'm finding that tables don't seem to auto convert to structs, which seems an odd omission. Hoping to get a more complete list of differences before they cause problems down the line.
I am also very curious how 64bit numbers are intended to be constructed, since LuaJIT has special syntax for it.