Dune-release 1.2.0

See full changelog
  • Remove assert false in favor of error message. (#125, @ejgallego)
  • Embed a 'version: "$release-version"' in each opam file of the current directory to get reproducible releases (#128, #129, @hannesm)
  • Generate sha256 and sha512 checksums for release (#131, @hannesm)
  • Grammar fixes (#132, @anmonteiro)
  • Handle doc fields with no trailing slash (#133, @yomimono)