[Spot] Number of states and transitions

Hi all,

I did not find how to get the number of states (reachable or not) of an automaton using autfilt (in particular the `--stats` option). The option provided by `autfilt --stats` is for reachable states only. I did find a workaround with `--hoaf` which outputs the automaton in HOA format and then getting the number from the `States:` header. For the number of transitions (reachable or not) I don't have a workaround.

Since spot can compute these numbers easily, it seems handy (at least for me) to have a direct access to them thru the `--stats` interface.

Thank you, Pierre.