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This removes lots of superfluous parentheses in the outer terms.

Extraction of C arrays

See merge request !88

Improve goals generated by the Gappa printer.

See merge request !103

Rework numerical constants.

See merge request !101

Main changes are:
- Real constants now offer a normalized representation usable for internal
  computations.
- Constants are no longer stored in textual form.

Put the three_idem example in the examples folder

See merge request !99

Factor abnormal transformation exceptions under is_fatal

Closes #275

See merge request !98

Also replace eprintf with Warning.emit in session_itp.

When reloading, fatal transformations should be notified to the user but
should not make the whole reload fail

Add the example about three-idempotent rings

See merge request !97

fix #274

Closes #274

See merge request !96

When applying a transformation without arguments, this checks that
arguments are indeed not provided. If they are, it now raises the same
exception as transformation with too many arguments.

Also update CHANGES with recent changes.