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Signed-off-by: Yann Regis-Gianas <yann@nomadic-labs.com>

- add a better fold function
- expose the Tree module
- remove duplicate context signatures

Note that clients include tezos-client, but also:
 - tezos-accuser
 - tezos-endorser
 - tezos-baker

Co-Authored-By: Clement Hurlin <clement.hurlin@tweag.io>

Irmin 2.3 hash changed the result of `Tree.list` to return a list
in a not specified order. So make sure we preserve the current
behavior of lib-storage:

- Nodes need their entries to be sorted before hashing them
- Context.fold need to go over the entries in a deterministic
  order to avoid issues with non-commutative operations over the
  context.

This commit:
- fix the pages: they used to all document the alpha version of the binaries
- renames the included HTML pages in the 008 documentation to not call
them "alpha"
- adds the pages for the alpha protocol