* 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.
* bench/stutter/stutter_bench.sh: Collect benchmarks for different
number of atomic propositions in a single csv file.
* bench/stutter/stutter.ipynb: Visualize benchmarks generated by
stutter_bench.sh.
