translate any automaton to a parity automaton

* spot/twaalgos/toparity.cc, spot/twaalgos/toparity.hh: implement it,
  based on last-appearance record (LAR)
* spot/twaalgos/Makefile.am: build it
* NEWS: document it
* python/spot/impl.i: add to python bindings
* tests/Makefile.am, tests/python/toparity.py: test it

spot/twaalgos/toparity.hh

@@ -0,0 +1,33 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) 2018 Laboratoire de Recherche et Développement
+// de l'Epita.
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <spot/twa/twagraph.hh>
+
+namespace spot
+{
+  /// \ingroup twa_acc_transform
+  /// \brief Take an automaton with any acceptance condition and return an
+  /// equivalent parity automaton.
+  ///
+  /// The parity condition of the returned automaton is max even.
+  SPOT_API twa_graph_ptr
+  to_parity(const const_twa_graph_ptr& aut, bool pretty_print=false);
+}