[selectors] match_kwargs and match_form_params selectors both accept a new `once_is_enough` argument (closes #1990438) also fix docstring of match_exception and references to selectors in the book.

#! /bin/sh -e
#

if [ "$1" = configure ]; then
  if which install-docs >/dev/null 2>&1; then
    install-docs -i /usr/share/doc-base/cubicweb-doc
  fi
fi


#DEBHELPER#

exit 0