Use voodoo_serialize to decode status.json and package.json

[sabine]

Voodoo now provides a module Voodoo_serialize that implements serialization/deserialization for status.json and package.json, so we use it, in order to promote the current documentation build from current to live.

Since the Voodoo_serialize types still differ slightly from the types in Ocamlorg_package, we have to "massage the data" between them. This will become simpler when tidying up on both (voodoo and ocaml.org) sides.