* spot/parseaut/parseaut.yy, spot/parseaut/scanaut.ll: Add rules for
PGSolver's format.
* spot/parseaut/public.hh: PGAME is a new type of output.
* tests/core/pgsolver.test: New file.
* tests/Makefile.am: Add it.
* tests/python/games.ipynb: More exemples.
* NEWS: Mention the new feature.
