Release Spot 2.3.1

* configure.ac, NEWS, doc/org/setup.org: Bump version numbers.

NEWS

-New in spot 2.3.0.dev (not yet released)
+New in spot 2.3.1 (2017-02-20)
 
   Tools:
 

configure.ac

@@ -21,7 +21,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 AC_PREREQ([2.61])
-AC_INIT([spot], [2.3.0.dev], [spot@lrde.epita.fr])
+AC_INIT([spot], [2.3.1], [spot@lrde.epita.fr])
 AC_CONFIG_AUX_DIR([tools])
 AC_CONFIG_MACRO_DIR([m4])
 AM_INIT_AUTOMAKE([1.11 gnu tar-ustar color-tests parallel-tests])

doc/org/setup.org

 #+OPTIONS: H:2 num:nil toc:t html-postamble:nil
 #+EMAIL: spot@lrde.epita.fr
 #+HTML_LINK_HOME: index.html
-#+MACRO: SPOTVERSION 2.3
-#+MACRO: LASTRELEASE 2.3
-#+MACRO: LASTTARBALL [[http://www.lrde.epita.fr/dload/spot/spot-2.3.tar.gz][=spot-2.3.tar.gz=]]
-#+MACRO: LASTNEWS [[https://gitlab.lrde.epita.fr/spot/spot/blob/spot-2-3/NEWS][summary of the changes]]
-#+MACRO: LASTDATE 2017-01-19
+#+MACRO: SPOTVERSION 2.3.1
+#+MACRO: LASTRELEASE 2.3.1
+#+MACRO: LASTTARBALL [[http://www.lrde.epita.fr/dload/spot/spot-2.3.1.tar.gz][=spot-2.3.1.tar.gz=]]
+#+MACRO: LASTNEWS [[https://gitlab.lrde.epita.fr/spot/spot/blob/spot-2-3-1/NEWS][summary of the changes]]
+#+MACRO: LASTDATE 2017-02-20