* spot/twaalgos/game.hh, spot/twaalgos/game.cc: Rename
solve_reachability_game() as solve_safety_game(), rewrite it (the old
implementation incorrectly marked dead states as winning for their
owner).
* tests/python/paritygame.ipynb: Rename as...
* tests/python/games.ipynb: ... this, and illustrate
solve_safety_game().
* tests/Makefile.am, NEWS, doc/org/tut.org: Adjust.
* tests/python/except.py: Add more tests.
* spot/misc/game.cc, spot/misc/game.hh: More efficient implementation
of Zielonka's algorithm to solve parity games. Now supports SCC
decomposition and efficient handling of certain special cases.
* doc/org/concepts.org: Document "strategy" and "state-winner"
properties.
* bin/ltlsynt.cc, tests/python/paritygame.ipynb: Adjust.
* tests/core/ltlsynt.test: Add more tests.
* python/spot/impl.i: Process game.hh.
* spot/misc/game.cc, spot/misc/game.hh: Make the output of
parity_game_solve() a solved_game object for easier manipulation in
Python.
* bin/ltlsynt.cc: Adjust usage.
* tests/python/paritygame.ipynb: New file.
* tests/Makefile.am, doc/org/tut.org: Add it.
* NEWS: Mention these bindings.
