switch to C++14 compilation

* 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.

doc/org/compile.org

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 #+TITLE: Compiling against Spot
-#+DESCRIPTION: How to compile C++11 programs using Spot
+#+DESCRIPTION: How to compile C++14 programs using Spot
 #+SETUPFILE: setup.org
 #+HTML_LINK_UP: tut.html
 
@@ -39,10 +39,10 @@ obvisously.  On this page, we are going to assume that you use =g++=
 same user interface.  To successfully build the =hello= program, we
 might need to tell the compiler several things:
 
-1. The language that we use is C++11 (or C++14).  This usually
-   requires passing an option like =-std=c++11=.  Note that with
-   version 6 of =g++= the default is now to compile C++14, so this
-   option is not necessary.
+1. The language that we use is C++14 (or optionally C++17).  This
+   usually requires passing an option like =-std=c++14=.  Note that
+   with version 6 of =g++= the default is now to compile C++14, so
+   this option is not necessary.
 2. The C++ preprocessor should be able to find =spot/misc/version.hh=.
    This might require appending another directory to the include
    search path with =-I location=.
@@ -78,7 +78,7 @@ be able to find everything by default, and you should be able to
 compile =hello.cc= and then execute =hello= with
 
 #+BEGIN_SRC sh
-g++ -std=c++11 hello.cc -lspot -o hello
+g++ -std=c++14 hello.cc -lspot -o hello
 ./hello
 #+END_SRC
 
@@ -101,11 +101,11 @@ This means that all spot headers have been installed in
 
 Usually, these directories are searched by default, so
 #+BEGIN_SRC sh
-g++ -std=c++11 hello.cc -lspot -o hello
+g++ -std=c++14 hello.cc -lspot -o hello
 #+END_SRC
 should still work.  But if that is not the case, add
 #+BEGIN_SRC sh
-g++ -std=c++11 -I/usr/local/include hello.cc -L/usr/local/lib -lspot -o hello
+g++ -std=c++14 -I/usr/local/include hello.cc -L/usr/local/lib -lspot -o hello
 #+END_SRC
 
 If running =./hello= fails with a message about not finding =libspot.so=,
@@ -131,7 +131,7 @@ libraries in =$HOME/usr/lib=.
 
 You would compile =hello.cc= with
 #+BEGIN_SRC sh
-g++ -std=c++11 -I$HOME/usr/include hello.cc -L$HOME/usr/lib -lspot -o hello
+g++ -std=c++14 -I$HOME/usr/include hello.cc -L$HOME/usr/lib -lspot -o hello
 #+END_SRC
 and execute with
 #+BEGIN_SRC sh
@@ -184,7 +184,7 @@ There are at least two traps with this scenario:
 
 So compiling against a non-installed Spot would look like this:
 #+BEGIN_SRC sh
-/dir/spot-X.Y/libtool link g++ -std=c++11 -I/dir/spot-X.Y -I/dir/spot-X.Y/buddy/src hello.cc /dir/spot-X.Y/spot/libspot.la -o hello
+/dir/spot-X.Y/libtool link g++ -std=c++14 -I/dir/spot-X.Y -I/dir/spot-X.Y/buddy/src hello.cc /dir/spot-X.Y/spot/libspot.la -o hello
 #+END_SRC
 
 Using =libtool link g++= instead of =g++= will cause =libtool= to

doc/org/concepts.org

@@ -1022,7 +1022,7 @@ components that are distributed and installed by Spot.
 
   - =libbddx= is a customized version of [[https://sourceforge.net/projects/buddy/][the BuDDy library]], for
     manipulating [[#bdd][BDDs]].
-  - =libspot= is the main library, containing a C++11 implementation of all the
+  - =libspot= is the main library, containing a C++14 implementation of all the
     data structures and algorithms.  This depends on =libddx=.
   - =libspotgen= is an auxiliary library that contains functions to
     generate families of automata, useful for benchmarking and testing
@@ -1034,7 +1034,7 @@ components that are distributed and installed by Spot.
     SpinS or a patched version of DiVinE, but you have to install
     those third-party tools first.  See [[https://gitlab.lrde.epita.fr/spot/spot/blob/next/tests/ltsmin/README][=tests/ltsmin/README=]]
     for details.
-  - In addition to the C++11 API, we also provide Python bindings for
+  - In addition to the C++14 API, we also provide Python bindings for
     =libspotgen=, =libspotltsmin=, =libbddx=, and most of =libspot=.
     These are available by importing =spot.gen=, =spot.ltsmin=, =bdd=,
     and =spot=.  Those Python bindings also includes some additional

doc/org/index.org

@@ -1,11 +1,11 @@
 # -*- coding: utf-8 -*-
 #+TITLE: Spot: a platform for LTL and ω-automata manipulation
 #+DESCRIPTION: Spot is a library and tool suite for LTL and ω-automata
-#+KEYWORDS: Spot,C++11,library,platform,framework,tool-suite,LTL,PSL,omega-automata
+#+KEYWORDS: Spot,C++14,library,platform,framework,tool-suite,LTL,PSL,omega-automata
 #+SETUPFILE: setup.org
 #+HTML_HEAD_EXTRA: <style>#org-div-home-and-up { display: none; }</style>
 
-Spot is a C++11 library for LTL, ω-automata manipulation and model
+Spot is a C++14 library for LTL, ω-automata manipulation and model
 checking.  It has the following notable features:
 
 - Support for [[file:concepts.org::#ltl][LTL]] (several syntaxes supported) and

doc/org/install.org

@@ -16,7 +16,7 @@ successful development build]].
 
 ** Requirements
 
-Spot requires a C++11-compliant compiler.  =g++= 4.8 or later, as well
+Spot requires a C++14-compliant compiler.  =g++= 5.0 or later, as well
 as =clang++= 3.5 or later should work.
 
 Spot expects a complete installation of Python (version 3.3 or later).
@@ -75,7 +75,7 @@ apt-get install spot libspot-dev spot-doc python3-spot # Or a subset of those
 #+END_SRC
 
 The package =spot= contains the [[file:tools.org][command-line tools]]. =libspot-dev=
-contains the header files if you plan to use Spot in a C++11
+contains the header files if you plan to use Spot in a C++14
 program. =spot-doc= contains some html (including these pages) and pdf
 documentation. Finally =python3-spot= contains some Python bindings
 (this package also installs some ipython notebooks that you can use as

doc/org/tut.org

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 #+TITLE: Code Examples
-#+DESCRIPTION: Directory of code examples for using Spot in C++11, Python, and shell.
+#+DESCRIPTION: Directory of code examples for using Spot in C++14, Python, and shell.
 #+SETUPFILE: setup.org
 #+HTML_LINK_UP: index.html
 

doc/org/upgrade2.org

@@ -20,7 +20,7 @@ experience of updating a couple of projects that are using Spot.
   Spot 1.2.6 and Spot 2.0, just to get an idea of what will need to be
   updated.
 
-  1. [[#cpp11][Spot now compiles using the C++11 standard]].  Compliant compiler
+  1. [[#cpp14][Spot now compiles using the C++14 standard]].  Compliant compiler
      are sufficiently widespread now that this should not be an issue.
 
   2. The layout of the source-tree and the layout of the installed
@@ -83,23 +83,22 @@ experience of updating a couple of projects that are using Spot.
      numbered.  Many algorithms have been rewritten on top of this
      =twa_graph= class, and this simplified them a lot.
 
-* Upgrading to C++11
+* Upgrading to C++14
   :PROPERTIES:
   :CUSTOM_ID: cpp11
   :END:
 
-  Because Spot now relies on C++11 features, programs that use Spot
+  Because Spot now relies on C++14 features, programs that use Spot
   should at least be compiled using this version (or a later one) of
   the language.
 
   Before the =g++= 6.0, the default C++ standard used was C++98, and
-  enabling C++11 is usually done by passing the option =-std=c++11=.
+  enabling C++14 is usually done by passing the option =-std=c++14=.
   In =g++= 6.0 the default C++ standard used is C++14, so passing
-  =-std=c++11= is only necessary in projects that are incompatible
-  with C++14.
+  =-std=c++14= is not necessary.
 
-  Upgrading from C++98 or C++03 to C++11 should be relatively smooth
-  as the language is /mostly/ backward compatible.
+  Upgrading from C++98, C++03 or C++11 to C++14 should be relatively
+  smooth as the language is /mostly/ backward compatible.
 
 * Upgrading =#include= directives
   :PROPERTIES:
@@ -600,7 +599,6 @@ for (auto i: aut->succ(s))
   automatically unregistered when the automaton is destroyed.
 
 
-
 * Various renamings
 
   :PROPERTIES: