stutter: fiddle with the benchmark
* bench/stutter/stutter_bench.sh: Add headers in the CSV files, and also run stutter_invariance_randomgraph. * bench/stutter/stutter_invariance_formulas.cc: Remove space from CSV output. * bench/stutter/stutter_invariance_randomgraph.cc: Likewise, plus fix the call to is_stutter_invariant(), and return an average time. * bench/stutter/stutter.ipynb: Adjust. * bench/stutter/README: Simplify. * bench/stutter/Makefile.am: Distribute the script and python notebook.