add two-phase commit example

[nano-o]

No description provided.

[nano-o]

This is a small example that worked maybe two weeks ago or so. Has the phase-automaton feature been removed from mypyvy?

[wilcoxjay]

We decided to remove the phase-automaton feature from the master branch because we were not planning to improve on our Phase-UPDR paper in the near future. Instead, we hope to focus on other improvements to UPDR.

I decided to remove the feature completely, but it would be relatively easy to support verification of phase automata, if you are interested in continuing to use that feature. What do you think?

[nano-o]

We wrote the 2pc example for our distributed systems reading group at Galois, but beyond that I don't have plans to use the feature at this point. It would be nice to keep an archived version of it somewhere though.