v3.5.0

CHANGES:

• Fix support for x-compilation (@samoht, #44)
• Update to dune.2.0 and apply ocamlformat (@samoht, #45)
• Select unsafe.ml only with dune (@emillon, #46)
• Remove indirect dependecy to ocamlfind (@kit-ty-kate, #49)
• Hide internals of base64 and return a string as the alphabet (@reynir, #48)
  breaking chnages Base64.alphabet is updated and return a simple string now