Use the integers package

[bbc2]

This follows the discussion in #446 about moving Signed and Unsigned to a separate module. Until now, they had only been copied. This pull request removes them from the ctypes package and adds a dependency to the integers package.

[bbc2]

Some remaining points:

• The ARM build fails. It looks like the Docker image is not provisioned with the integers package.
• The Android build fails. It looks like ocamlfind can't find the integers package despite it being installed. I don't know why.

[yallop]

I'm working on a fix for the ARM build now.

[yallop]

The ARM build is fixed. I'm not sure yet what's wrong with the Android build. Perhaps the integers package needs some work to support cross-compilation.

[yallop]

#517 should fix the problems with the Appveyor (Windows) builds.

[bbc2]

Cool! I tested a rebased version on a different branch and the Appveyor build succeeded.

[yallop]

Could you rebase this branch, too, now that #517 is merged?

[yallop]

@whitequark: do you have any idea what might be needed to fix the Android build? The ctypes build logs have

# ocamlfind: Package `integers' not found

after integers has been installed successfuly. Does the integers package need some ocamlfind adjustments (e.g. with -toolchain android) to support cross-compilation?

[whitequark]

One would think. Where's the repo of integers?

[yallop]

https://github.com/ocamllabs/ocaml-integers

[whitequark]

@yallop Well yeah, someone would need to package integers for opam-cross-android.

[yallop]

@whitequark: ocaml-cross/opam-cross-android#31

[whitequark]

opam-cross-android PR merged

[yallop]

Thanks, @whitequark.

@bbc2: I've pushed a commit (bc67d2f) to your branch which I hope fixes the Android build.

[bbc2]

Thank you for fixing the builds. It looks good to me now.

[yallop]

Thank you for the contribution, @bbc2!