[debian] build the book with no auto-compression of book files (closes: #1906581) Book content paths (html and rest) are now excluded from Debian compression step. This will fix a documentation search issue on the website (doc.cubicweb.org) Documentation build is now made optional since it can break for old distributions and we don't want to block a new release of Cubicweb because of documentation issues.

# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
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"""%(distname)s entity's classes"""