Start work on algorithm to display the shortest path to a state
Merge branch 'master' into path_to

Conflicts:
	pnmc/mc/classic/firing_rule.cc
	pnmc/mc/classic/firing_rule.hh
	pnmc/mc/classic/worker.cc
	pnmc/mc/shared/statistics.hh
	pnmc/mc/shared/statistics_serialize.hh
Rename classic and rewritten homomorphisms
Fast exit even if the computation is interrupted
Finalize merge
Full path_to algorithm.
Remove redundant homomorphism
tmp
Merge branch 'master' into path_to

Conflicts:
	pnmc/mc/classic/worker.cc
Fully functional trace algorithm

But awfully slow...
Make trace option an hidden feature, it's still too slow