Add new benchmarks

Over the last week, the implementation has undergone several improvements.
A notable bug fix is in commit 83198ebe1d4fe807afff39316afde04f910f77e6.
We found that this slowed down the implementation. We therefore rerun Seed
to randomly generate around 2000 benchmarks consisting of pairs of programs
of size 15. We then run these benchmarks with Z3 in less than 24 hours and
selected those that took more than 3 seconds to complete and involving at
least one SMT solver call. The raw benchmark results are included here.