* configure.ac: Compile in C++14 by default and rename
--enable-c++14 as c++17.
* doc/org/compile.org, doc/org/concepts.org, doc/org/index.org,
doc/org/install.org, doc/org/tut.org, doc/org/upgrade2.org, HACKING,
NEWS, README: Adjust all mentions of C++11.
* spot/twaalgos/stats.hh: Use std::make_unique.
Part of #176.
* doc/org/autfilt.org, doc/org/compile.org, doc/org/concepts.org,
doc/org/csv.org, doc/org/dstar2tgba.org, doc/org/genltl.org,
doc/org/hoa.org, doc/org/install.org, doc/org/ioltl.org,
doc/org/ltl2tgba.org, doc/org/ltl2tgta.org, doc/org/ltlcross.org,
doc/org/ltldo.org, doc/org/ltlfilt.org, doc/org/ltlgrind.org,
doc/org/oaut.org, doc/org/randaut.org, doc/org/randltl.org,
doc/org/satmin.org, doc/org/tools.org, doc/org/tut.org,
doc/org/tut01.org, doc/org/tut02.org, doc/org/tut03.org,
doc/org/tut10.org, doc/org/tut20.org, doc/org/tut21.org,
doc/org/tut22.org, doc/org/tut30.org, doc/org/upgrade2.org: Here.
* doc/org/index.org: Also add keywords in case it is useful, and
use a more descripting title for search engines.
* doc/org/install.org: New file.
* doc/Makefile.am: Add it.
* doc/org/index.org: Link to it.
* doc/org/setup.org: Add macro for
various version numbers.
* doc/org/tools.org: Update version number.
* NEWS, README, bench/ltl2tgba/README, debian/control,
debian/copyright: Update URLs to website.
