implement SVA's first_match operator

* NEWS, doc/tl/tl.tex, doc/tl/tl.bib: Document it.
* spot/parsetl/parsetl.yy, spot/parsetl/scantl.ll: Parse it.
* spot/tl/formula.cc, spot/tl/formula.hh, spot/tl/dot.cc,
spot/tl/mutation.cc, spot/tl/print.cc, spot/tl/randomltl.cc,
spot/twaalgos/ltl2tgba_fm.cc: Adjust to support first_match.
* spot/tl/mark.cc, spot/tl/simplify.cc, spot/tl/snf.cc,
spot/tl/unabbrev.cc, spot/twa/formula2bdd.cc,
spot/twaalgos/ltl2taa.cc: Ignore it.
* tests/core/acc_word.test, tests/core/randpsl.test: Add more tests.
* tests/core/rand.test, tests/core/unambig.test,
tests/python/randltl.ipynb: Adjust.
* tests/python/formulas.ipynb: Show first_match.

tests/core/randpsl.test

@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2011, 2012, 2014, 2015, 2016 Laboratoire de Recherche
+# Copyright (C) 2011, 2012, 2014, 2015, 2016, 2019 Laboratoire de Recherche
 # et Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -25,10 +25,15 @@ set -e
 
 # Generate 50 random unique PSL formula that do not simplify to LTL
 # formulae, and that have a size of at least 12.
-randltl -n -1 --tree-size 30 --seed 12 --psl a b c |
+# The seed is selected so the test is fast enough, feel free to
+# adjust it whenever something changes in formula generation.
+randltl -n -1 --tree-size 30 --seed 13 --psl a b c |
 ltlfilt -r --size 12.. --unique |
 ltlfilt -v --ltl -n 50 | tee formulas |
 ltlcross '../ikwiad -R3 -t %f >%T' '../ikwiad -x -R3 -t %f >%T' \
   -F - -f '{{(p1)}[*]:{(p3) && {{!(p1)} xor {!(p3)}}}}'
 
 test `wc -l < formulas` = 50
+
+
+randltl --psl --sere-priorities=first_match=10 -n 100 2 | grep first_match