extend HOA I/O to preserve the state-player property

* spot/parseaut/parseaut.yy, spot/parseaut/scanaut.ll,
spot/twaalgos/hoa.cc: Add input and output support.
* doc/org/hoa.org: Document the HOA extension.
* bin/ltlsynt.cc: Add a --print-game-hoa option to
produce such format.
* tests/core/gamehoa.test: New file to test this.
* tests/Makefile.am: Add it.
* NEWS: Mention this new feature.

doc/org/hoa.org

@@ -1154,3 +1154,69 @@ rm -f stvstracc.hoa sba.hoa stvstrlab.hoa decorate.hoa
 #  LocalWords:  bitsets randaut stvstrlab aut Hv hw bigwedge mathsf
 #  LocalWords:  genltl gf GFp Fp parser's rankdir br labelloc ffffa
 #  LocalWords:  fillcolor fontname svg txt Xa
+** Arenas for two-player games
+
+An automaton can be seen as a two-player game by simply annotating
+states with number representing the player that should play in this
+state.  We use an extension to the HOA format to transmit this
+information: the =spot-state-player:= head (or =spot.state-player:= when
+using the HOA 1.1 version) is followed by a string of =0= or
+=1=, one per state of the automaton, representing the player's number
+associated to each state.
+
+For instance in the following output of =ltlsynt=, the sequence
+call_player() indicates the players owning each of the
+call_player(h="States")[:results raw] states.
+
+#+NAME: exgame
+#+begin_src sh :wrap SRC hoa
+ltlsynt --ins=a --outs=b -f 'Ga <-> Gb' --print-game-hoa
+#+end_src
+
+#+RESULTS: exgame
+#+begin_SRC hoa
+HOA: v1
+States: 11
+Start: 3
+AP: 2 "a" "b"
+acc-name: Streett 1
+Acceptance: 2 Fin(0) | Inf(1)
+properties: trans-labels explicit-labels trans-acc colored complete
+properties: deterministic
+spot-state-player: 0 0 0 0 1 1 1 1 1 1 0
+--BODY--
+State: 0
+[t] 4 {0}
+State: 1
+[t] 5 {0}
+State: 2
+[0] 6 {0}
+[!0] 7 {0}
+State: 3
+[0] 8 {0}
+[!0] 5 {0}
+State: 4
+[t] 0 {1}
+State: 5
+[!1] 0 {0}
+[1] 1 {0}
+State: 6
+[t] 2 {0}
+State: 7
+[t] 0 {0}
+State: 8
+[!1] 2 {0}
+[1] 3 {1}
+State: 9
+[t] 10 {0}
+State: 10
+[t] 9 {0}
+--END--
+#+end_SRC
+
+#+NAME: player
+#+BEGIN_SRC sh :exports none :var t=exgame h="spot-state-player"
+sed -n "s/^$h: \(.*\)\$/\\1/p" <<EOF  | tr -d '\n'
+$t
+EOF
+#+END_SRC