1.0.0

CHANGES:

• Migrate scrypt from Cstruct.t to string
• Merge ocaml-pbkdf (from https://github.com/abeaumont/ocaml-pbkdf),
  hkdf (from https://github.com/hannesm/ocaml-hkdf), and scrypt (from
  https://github.com/abeaumont/ocaml-scrypt-kdf) into a single repository
  and opam package (with three subpackages, kdf.pbkdf. kdf.hkdf, and
  kdf.scrypt).
• Disable a failing testcase for architectures with integers no longer than 31
  bits (thanks to @kit-ty-kate)