parseaut: Add support for PGSolver's format
- 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.