Update bitstring sources

[CharlesAverill]

Old versions of the bitstring package pointed their source to a now-defunct Bitbucket repository. This PR updates the sources to the currently-maintained Github repository https://github.com/xguerin/bitstring

[mseri]

Looks like some checksums are different. We should try to get the old packages from the caches: https://github.com/ocaml/opam-repository/wiki/FAQ#how-to-find-lost-archives-of-packages

[shonfeder]

@mseri I was not able to find this source in any of the archives using the recipes in https://github.com/ocaml/opam-repository/wiki/FAQ#how-to-find-lost-archives-of-packages

E.g., I've tried

• https://opam.robur.coop/cache/sha256/a8/a848f15787709e88bf97a81d5e7dc0115ad83b3cf36bbaec6a69fdf3d102f7bd
• https://gitlab.ocamlpro.com/OCamlPro/opam-repository/-/tree/cached/cache/sha256/a8/a848f15787709e88bf97a81d5e7dc0115ad83b3cf36bbaec6a69fdf3d102f7bd
• https://opam.ocaml.org/cache/sha256/a8/a848f15787709e88bf97a81d5e7dc0115ad83b3cf36bbaec6a69fdf3d102f7bd
• https://opam.ocaml.org/cache/md5/70/70f7acebe337072bff03a1f7a3fb1d3a

Do we have any other option (or might I be making a mistake with with the construction of the URLs)? Or will we need to accept a changed checksum if this is to remain available?

[kit-ty-kate]

those archives should probably be uploaded to https://github.com/ocaml/opam-source-archives/ instead of relying on ocamlpro's repository

[shonfeder]

Ah ok, makes sense. I'll do that when I have a moment.

Could you (or someone with perms) update https://github.com/ocaml/opam-repository/wiki/FAQ#how-to-find-lost-archives-of-packages so that the need for adding the sources to the archive in such cases is recorded?

[mseri]

Done

[mseri]

Sources are now all accessible

[shonfeder]

Thanks for picking this up!