comportement was not very clear if an exception was raised.

 (metas, debug flags, transformations, formats) except for label.

This description is used in --list-*. The description can use any of
the formatting markup of Format "@ " "@[",...

Transformations can also specify from which metas and labels they
depend, and add informations about how they are interpreted.

TODO:
  - complete and correct the documentation
  - when a transformation use Trans.on_meta, it should be possible to
    add an interpretation of the metas in the documentation.
  - recover a summary version of --list-* ?
  - be able to export in latex?

  session pairing doesn't compute anymore the shape of the goal, it is
 done before. It was able to compute the shape only when the checksum
 of the task was different, but computing the checksum of the task is
 way more time consuming than computing the shape of the goal (and
 include it).

 So this commit simplify greatly the function and theoretically
 augment just a little the time spent. Experimentaly it's the inverse
 on max_matrix. Until "update_session: done" with or without modifying
 the checksums:

            before     |   after
without : 0.21-0.22 s  | 0.16-0.17 s
with    : 0.23-0.26 s  | 0.18-0.20 s

the index in the hastbl of proofs on parent goal must be
changed too

The goal is to keep track of unexpected termination, especially when the
output of the prover is empty.

- change takes function as the first argument
- add_new takes exception as the first argument
- find_default is renamed to find_def and takes the default value
  as the first argument
- find_option is renamed to find_opt (to align with find_exn and find_def)
- default_option is renamed def_option

Thanks to Johannes Kanig for this useful suggestion.

print all the edited files which appear in the session.

In conjonction with --print0 which prints '\000' instead of '\n' that
give a safe way to "git add" all the edited files of a session:

why3session info --edited-files --print0 vstte12_bfs.mlw |xargs -0 git add

Since why3session accept the why3session.xml (it uses the basename as
 session directory) you can add all the edited file of all the session
saved in a git repository with:

git ls-files -z |grep -z -e "why3session.xml$" |xargs -0 why3session info --edited-files --print0 | xargs -0 git add

? not verified (or not valid for proof_attempt)
! InternalFailure
O obsolete
A archived

It's goal is to allow to view and modify sessions.

Currently three sub-commands :
info : can give the provers used, pretty-print in ascii a session,
     can give the corresponding directory
mod : allow to set obsolete, or modify the archive state of proof attempt
    which corresponds to selected provers
copy : copy a proof attempt by modifing its prover

If a proof_attempt is archived, it is not replayed nor set obsolete.

Prover ids are only used for the command line option "-P".
The user can choose what he wants (they must be unique)
The prover name and version should not be modified. If someone want to
test different command line options for a prover he can use the
"alternative" field.

If someone want to replay an external proof but he doesn't have the
corresponding prover (same name,version,alternative), why3ide ask for
a replacement among the known provers. The choice can be saved.

 - create a session if the directory doesn't exists
 - If the directory exists but the xml doesn't behave as if the xml is empty.

Split session in two :
Session : an API for managing session without running provers
Session_scheduler : an API for running provers asynchronously

All the global states have been removed.

A session must be first read, which give a session without task.
Afterward it must be updated to the current state of the files with
some environnement and configuration.

printer and iterator are provided for session.

Session_tools : some useful functions on session.

Smoke detector : not anymore integrated to session. Just add the
      transformation "smoke_detector_top" or "smoke_detector_deep" to
      all the valid proof attempt.

prover_id are not yet removed but all is in place in session for that.