* spot/twaalgos/synthesis.cc, spot/twaalgos/synthesis.hh: New files
regrouping the functionnalities split and apply_strategy for synthesis
* python/spot/impl.i, spot/twaalgos/Makefile.am: Add them.
* spot/twaalgos/split.cc, spot/twaalgos/split.hh: No longer contains
the splits necessary for for synthesis, moved to
spot/twaalgos/synthesis.cc, spot/twaalgos/split.hh Split is now faster
and reduces the number of intermediate states, reducing the overall
size of the arena
* spot/misc/game.cc, spot/misc/game.hh: Renaming propagate_players to
alternate_players.
* tests/core/ltlsynt.test, tests/python/split.py: Update tests.
* bin/ltlsynt.cc: Adjust to new split. Swap order of split and
to_parity for lar.
Improve the way transitions are duplicated when preparing the turn-based
game for synthesis. The resulting arena should now be deterministic on
nodes owned by the environment. Also move the code to another file, so
that it is easier to test (e.g. in Python).
* bin/ltlsynt.cc: move the code
* spot/twaalgos/split.cc, spot/twaalgos/split.hh: move the code and
implement the improvements
* tests/Makefile.am, tests/python/split.py: test it
* tests/core/ltlsynt.test: update existing tests to reflect the changes