* spot/twaalgos/stutter.cc, spot/twaalgos/stutter.hh: Implement
stutter-invariance detection at the state level.
* python/spot/impl.i: Instantiate std::vector<bool>
* tests/python/stutter-inv-states.ipynb: New file.
* tests/Makefile.am, doc/org/tut.org: Add it.
