This is a LEGACY subdirectory meant to allow building 3d with
EverCrypt instead of ocaml-sha.

Since https://github.com/hacl-star/hacl-star/pull/784 was
merged, 3d now uses ocaml-sha instead, and building 3d with EverCrypt
is no longer officially supported. Thus:

* if you want to use this subdirectory, you will need to manually
  modify ../dune to exclude the sha/ subdirectory and include this one
  instead, and to declare a package dependency to hacl-star instead of
  sha

* this subdirectory is no longer maintained, so if there are any
  upstream changes in the EverCrypt OCaml bindings, then this
  subdirectory will not be updated and may even be removed.
