Even though `Int` and `isize` should be the same in practice, we can't cleanly convert, as the type information isn't quite there. And anyway, strictly speaking per the report, `Int` is only guaranteed to hold 30 bits.
Note that this is essentially unchanged even if we specify `usize_is_size_t = true` for `cbindgen`.
We drop the tools specifically designed for Haskell and Rust together, in favour of general tools for using each with C.
Namely, we use Mozilla's `cbindgen` for generating header files from the Rust source, and Well-Typed's new `hs-bindgen` tool for generating Haskell from those header files.
The Rust code here is essentially the result of expanding the old macro, then inlining and renaming internals.
The most important thing here is that we're now relying solely on robust well-maintained tools.
