[ocaml-ctypes] ANN: ctypes 0.12.0

[Jeremy Yallop]

I'm happy to announce a new release of ctypes, 0.12.0, available for
installation via OPAM.

Ctypes 0.12.0 contains a number of changes, some of which introduce
small incompatibilities with previous releases:

 * Support for Fortran-layout bigarrays

   Recently discussed here:
    http://lambda-diode.com/software/ocaml/scientific/fortran
    https://www.reddit.com/r/ocaml/comments/6azyv3/interfacing_fortran_with_ocaml/
    https://github.com/ocamllabs/ocaml-ctypes/issues/509

   The design is described here:
    https://github.com/ocamllabs/ocaml-ctypes/pull/523

 * Use the 'integers' package to provide signed and unsigned types

    https://github.com/ocamllabs/ocaml-ctypes/issues/446
    https://github.com/ocamllabs/ocaml-ctypes/pull/515

In both cases the types have changed slightly, but the behaviour is
unchanged, so code that continues to build with the new release should
be unaffected.

The release notes have further details of the changes in this release
and in recent point releases:

   https://github.com/ocamllabs/ocaml-ctypes/blob/0.12.0/CHANGES.md