Add non-breaking spaces and fix titles

- add unicode directive as substitution in conf.py and remove spaces around
  substitution (:trim:)
- add non-breaking spaces before double punctuation (; : ? «  » and !), except
  where non applicable (links, italics, code snippets, etc.)
- fix title adornments
- fix tables
- remove colon from titles

Signed-off-by: Olivier Carrère <carrereo@gmail.com>
Acked-by: Angela Cristina <acristina@redaction-technique.org>